Convert a lot of 'int' variables to 'bool'.

My normal habit these days, in new code, is to treat int and bool as
_almost_ completely separate types. I'm still willing to use C's
implicit test for zero on an integer (e.g. 'if (!blob.len)' is fine,
no need to spell it out as blob.len != 0), but generally, if a
variable is going to be conceptually a boolean, I like to declare it
bool and assign to it using 'true' or 'false' rather than 0 or 1.

PuTTY is an exception, because it predates the C99 bool, and I've
stuck to its existing coding style even when adding new code to it.
But it's been annoying me more and more, so now that I've decided C99
bool is an acceptable thing to require from our toolchain in the first
place, here's a quite thorough trawl through the source doing
'boolification'. Many variables and function parameters are now typed
as bool rather than int; many assignments of 0 or 1 to those variables
are now spelled 'true' or 'false'.

I managed this thorough conversion with the help of a custom clang
plugin that I wrote to trawl the AST and apply heuristics to point out
where things might want changing. So I've even managed to do a decent
job on parts of the code I haven't looked at in years!

To make the plugin's work easier, I pushed platform front ends
generally in the direction of using standard 'bool' in preference to
platform-specific boolean types like Windows BOOL or GTK's gboolean;
I've left the platform booleans in places they _have_ to be for the
platform APIs to work right, but variables only used by my own code
have been converted wherever I found them.

In a few places there are int values that look very like booleans in
_most_ of the places they're used, but have a rarely-used third value,
or a distinction between different nonzero values that most users
don't care about. In these cases, I've _removed_ uses of 'true' and
'false' for the return values, to emphasise that there's something
more subtle going on than a simple boolean answer:
 - the 'multisel' field in dialog.h's list box structure, for which
   the GTK front end in particular recognises a difference between 1
   and 2 but nearly everything else treats as boolean
 - the 'urgent' parameter to plug_receive, where 1 vs 2 tells you
   something about the specific location of the urgent pointer, but
   most clients only care about 0 vs 'something nonzero'
 - the return value of wc_match, where -1 indicates a syntax error in
   the wildcard.
 - the return values from SSH-1 RSA-key loading functions, which use
   -1 for 'wrong passphrase' and 0 for all other failures (so any
   caller which already knows it's not loading an _encrypted private_
   key can treat them as boolean)
 - term->esc_query, and the 'query' parameter in toggle_mode in
   terminal.c, which _usually_ hold 0 for ESC[123h or 1 for ESC[?123h,
   but can also hold -1 for some other intervening character that we
   don't support.

In a few places there's an integer that I haven't turned into a bool
even though it really _can_ only take values 0 or 1 (and, as above,
tried to make the call sites consistent in not calling those values
true and false), on the grounds that I thought it would make it more
confusing to imply that the 0 value was in some sense 'negative' or
bad and the 1 positive or good:
 - the return value of plug_accepting uses the POSIXish convention of
   0=success and nonzero=error; I think if I made it bool then I'd
   also want to reverse its sense, and that's a job for a separate
   piece of work.
 - the 'screen' parameter to lineptr() in terminal.c, where 0 and 1
   represent the default and alternate screens. There's no obvious
   reason why one of those should be considered 'true' or 'positive'
   or 'success' - they're just indices - so I've left it as int.

ssh_scp_recv had particularly confusing semantics for its previous int
return value: its call sites used '<= 0' to check for error, but it
never actually returned a negative number, just 0 or 1. Now the
function and its call sites agree that it's a bool.

In a couple of places I've renamed variables called 'ret', because I
don't like that name any more - it's unclear whether it means the
return value (in preparation) for the _containing_ function or the
return value received from a subroutine call, and occasionally I've
accidentally used the same variable for both and introduced a bug. So
where one of those got in my way, I've renamed it to 'toret' or 'retd'
(the latter short for 'returned') in line with my usual modern
practice, but I haven't done a thorough job of finding all of them.

Finally, one amusing side effect of doing this is that I've had to
separate quite a few chained assignments. It used to be perfectly fine
to write 'a = b = c = TRUE' when a,b,c were int and TRUE was just a
the 'true' defined by stdbool.h, that idiom provokes a warning from
gcc: 'suggest parentheses around assignment used as truth value'!

ssh2connection-server.c

@@ -79,7 +79,7 @@ ChanopenResult ssh2_connection_parse_channel_open(
     }
 }
 
-int ssh2_connection_parse_global_request(
+bool ssh2_connection_parse_global_request(
     struct ssh2_connection_state *s, ptrlen type, PktIn *pktin)
 {
     if (ptrlen_eq_string(type, "tcpip-forward")) {
@@ -88,14 +88,14 @@ int ssh2_connection_parse_global_request(
         /* In SSH-2, the host/port we listen on are the same host/port
          * we want reported back to us when a connection comes in,
          * because that's what we tell the client */
-        int toret = portfwdmgr_listen(
+        bool toret = portfwdmgr_listen(
             s->portfwdmgr, host, port, host, port, s->conf);
         sfree(host);
         return toret;
     } else if (ptrlen_eq_string(type, "cancel-tcpip-forward")) {
         char *host = mkstr(get_string(pktin));
         unsigned port = get_uint32(pktin);
-        int toret = portfwdmgr_unlisten(s->portfwdmgr, host, port);
+        bool toret = portfwdmgr_unlisten(s->portfwdmgr, host, port);
         sfree(host);
         return toret;
     } else {
@@ -200,19 +200,19 @@ SshChannel *ssh2_serverside_agent_open(ConnectionLayer *cl, Channel *chan)
     return &c->sc;
 }
 
-void ssh2channel_start_shell(SshChannel *sc, int want_reply)
+void ssh2channel_start_shell(SshChannel *sc, bool want_reply)
 {
     assert(false && "Should never be called in the server");
 }
 
 void ssh2channel_start_command(
-    SshChannel *sc, int want_reply, const char *command)
+    SshChannel *sc, bool want_reply, const char *command)
 {
     assert(false && "Should never be called in the server");
 }
 
-int ssh2channel_start_subsystem(
-    SshChannel *sc, int want_reply, const char *subsystem)
+bool ssh2channel_start_subsystem(
+    SshChannel *sc, bool want_reply, const char *subsystem)
 {
     assert(false && "Should never be called in the server");
 }
@@ -229,7 +229,7 @@ void ssh2channel_send_exit_status(SshChannel *sc, int status)
 }
 
 void ssh2channel_send_exit_signal(
-    SshChannel *sc, ptrlen signame, int core_dumped, ptrlen msg)
+    SshChannel *sc, ptrlen signame, bool core_dumped, ptrlen msg)
 {
     struct ssh2_channel *c = container_of(sc, struct ssh2_channel, sc);
     struct ssh2_connection_state *s = c->connlayer;
@@ -244,7 +244,7 @@ void ssh2channel_send_exit_signal(
 }
 
 void ssh2channel_send_exit_signal_numeric(
-    SshChannel *sc, int signum, int core_dumped, ptrlen msg)
+    SshChannel *sc, int signum, bool core_dumped, ptrlen msg)
 {
     struct ssh2_channel *c = container_of(sc, struct ssh2_channel, sc);
     struct ssh2_connection_state *s = c->connlayer;
@@ -259,36 +259,36 @@ void ssh2channel_send_exit_signal_numeric(
 }
 
 void ssh2channel_request_x11_forwarding(
-    SshChannel *sc, int want_reply, const char *authproto,
-    const char *authdata, int screen_number, int oneshot)
+    SshChannel *sc, bool want_reply, const char *authproto,
+    const char *authdata, int screen_number, bool oneshot)
 {
     assert(false && "Should never be called in the server");
 }
 
-void ssh2channel_request_agent_forwarding(SshChannel *sc, int want_reply)
+void ssh2channel_request_agent_forwarding(SshChannel *sc, bool want_reply)
 {
     assert(false && "Should never be called in the server");
 }
 
 void ssh2channel_request_pty(
-    SshChannel *sc, int want_reply, Conf *conf, int w, int h)
+    SshChannel *sc, bool want_reply, Conf *conf, int w, int h)
 {
     assert(false && "Should never be called in the server");
 }
 
-int ssh2channel_send_env_var(
-    SshChannel *sc, int want_reply, const char *var, const char *value)
+bool ssh2channel_send_env_var(
+    SshChannel *sc, bool want_reply, const char *var, const char *value)
 {
     assert(false && "Should never be called in the server");
 }
 
-int ssh2channel_send_serial_break(SshChannel *sc, int want_reply, int length)
+bool ssh2channel_send_serial_break(SshChannel *sc, bool want_reply, int length)
 {
     assert(false && "Should never be called in the server");
 }
 
-int ssh2channel_send_signal(
-    SshChannel *sc, int want_reply, const char *signame)
+bool ssh2channel_send_signal(
+    SshChannel *sc, bool want_reply, const char *signame)
 {
     assert(false && "Should never be called in the server");
 }