New timing infrastructure. There's a new function schedule_timer()

which pretty much any module can call to request a call-back in the
future. So terminal.c can do its own handling of blinking, visual
bells and deferred screen updates, without having to rely on
term_update() being called 50 times a second (fixes: pterm-timer);
and ssh.c and telnet.c both invoke a new module pinger.c which takes
care of sending keepalives, so they get sent uniformly in all front
ends (fixes: plink-keepalives, unix-keepalives).

[originally from svn r4906]
[this svn revision also touched putty-wishlist]

windows/winnet.c

@@ -1353,6 +1353,16 @@ SOCKET next_socket(int *state)
     return s ? s->s : INVALID_SOCKET;
 }
 
+extern int socket_writable(SOCKET skt)
+{
+    Actual_Socket s = find234(sktree, (void *)skt, cmpforsearch);
+
+    if (s)
+	return bufchain_size(&s->output_data) > 0;
+    else
+	return 0;
+}
+
 int net_service_lookup(char *service)
 {
     struct servent *se;