Fixes for Debian bug #192701 (64-bit gccs warn about casts between

ptrs and ints of different size and -Werror makes this serious).
The GTK bits are done by Colin's patch to use GINT_TO_POINTER
(thanks); the uxnet bits are done by cleaning up the rest of the
code. In particular, network.h now typedefs `OSSocket' to be a type
capable of holding whatever the OS's socket data type is that
underlies our socket abstraction. Individual platforms can make this
typedef themselves if they define OSSOCKET_DEFINED to prevent
network.h redoing it; so the Unix OSSocket is now int. Default is
still void *, so other platforms should be unaffected.

[originally from svn r3171]

proxy.h

@@ -77,7 +77,7 @@ struct Socket_proxy_tag {
     int sent_bufsize;
 
     /* accepting */
-    void *accepting_sock;
+    OSSocket accepting_sock;
 
     /* configuration, used to look up proxy settings */
     Config cfg;