Change type of CONF_username to the new CONF_TYPE_STR_AMBI.

This is the pathfinding change that proves it's possible for _one_
Conf setting to become Unicode-capable.

That seems like quite a small reward for all the refactoring in the
previous patches this week! But changing over one configuration
setting is enough to get started with: once all the bugs are out of
this one, we can try switching over some more.

Changing the type to CONF_TYPE_STR_AMBI is enough by itself to make
the configuration dialog box write it into Conf as UTF-8, because
conf_editbox_handler automatically checks whether that possibility is
available. However, setting the same Conf entry from the command line
isn't automatic: I had to add code in the handler for the -l
command-line option in cmdline.c.

This commit also doesn't yet handle the _other_ way to specify a
username on the command line: including it as part of the hostname
argument via "putty user@host" or similar. That's more difficult,
because it also requires deciding what to do about UTF-8 in the actual
hostname.

(That looks as if it ought to be possible: Windows should be able to
handle looking up Unicode hostnames if you use GetAddrInfoW() in place
of getaddrinfo(). But plumbing it through everything in between
cmdline.c and windows/network.c is a bigger job than I'm prepared to
do in this proof-of-concept commit.)

cmdline.c

@@ -195,6 +195,7 @@ int cmdline_process_param(CmdlineArg *arg, CmdlineArg *nextarg,
 {
     int ret = 0;
     const char *p = cmdline_arg_to_str(arg);
+    const char *value_utf8 = cmdline_arg_to_utf8(nextarg);
     const char *value = cmdline_arg_to_str(nextarg);
 
     if (p[0] != '-') {
@@ -459,7 +460,10 @@ int cmdline_process_param(CmdlineArg *arg, CmdlineArg *nextarg,
         RETURN(2);
         UNAVAILABLE_IN(TOOLTYPE_NONNETWORK);
         SAVEABLE(0);
-        conf_set_str(conf, CONF_username, value);
+        if (value_utf8)
+            conf_set_utf8(conf, CONF_username, value_utf8);
+        else
+            conf_set_str(conf, CONF_username, value);
     }
     if (!strcmp(p, "-loghost")) {
         RETURN(2);

conf.h

@@ -444,7 +444,7 @@ CONF_OPTION(environmt,
     LOAD_CUSTOM, SAVE_CUSTOM, /* necessary for mappings */
 )
 CONF_OPTION(username,
-    VALUE_TYPE(STR),
+    VALUE_TYPE(STR_AMBI),
     DEFAULT_STR(""),
     SAVE_KEYWORD("UserName"),
 )

pscp.c

@@ -391,7 +391,7 @@ static void do_cmd(char *host, char *user, char *cmd)
     /* Set username */
     if (user != NULL && user[0] != '\0') {
         conf_set_str(conf, CONF_username, user);
-    } else if (conf_get_str(conf, CONF_username)[0] == '\0') {
+    } else if (conf_get_str_ambi(conf, CONF_username, NULL)[0] == '\0') {
         user = get_username();
         if (!user)
             bump("Empty user name");

settings.c

@@ -112,7 +112,9 @@ const struct BackendVtable *backend_vt_from_proto(int proto)
 
 char *get_remote_username(Conf *conf)
 {
-    char *username = conf_get_str(conf, CONF_username);
+    /* We don't worry about whether the username is stored as UTF-8,
+     * because SSH wants it as UTF-8 */
+    char *username = conf_get_str_ambi(conf, CONF_username, NULL);
     if (*username) {
         return dupstr(username);
     } else if (conf_get_bool(conf, CONF_username_from_env)) {

test/test_conf.c

@@ -717,7 +717,7 @@ void test_simple(void)
     test_bool_simple(CONF_ssh_no_shell, "SshNoShell", false);
     test_str_simple(CONF_termtype, "TerminalType", "xterm");
     test_str_simple(CONF_termspeed, "TerminalSpeed", "38400,38400");
-    test_str_simple(CONF_username, "UserName", "");
+    test_str_ambi_simple(CONF_username, "UserName", "", false);
     test_bool_simple(CONF_username_from_env, "UserNameFromEnvironment", false);
     test_str_simple(CONF_localusername, "LocalUserName", "");
     test_bool_simple(CONF_rfc_environ, "RFCEnviron", false);

unix/plink.c

@@ -823,7 +823,7 @@ int main(int argc, char **argv)
      * If we have no better ideas for the remote username, use the local
      * one, as 'ssh' does.
      */
-    if (conf_get_str(conf, CONF_username)[0] == '\0') {
+    if (conf_get_str_ambi(conf, CONF_username, NULL)[0] == '\0') {
         char *user = get_username();
         if (user) {
             conf_set_str(conf, CONF_username, user);