add a macro to ease conditional testing based on active window port

Add WINDOWPORT macro

example:
if (WINDOWPORT("tty"))
	pline("Look at me, I'm on tty at the moment!");

include/winprocs.h

@@ -260,6 +260,11 @@ struct wc_Opt {
     unsigned long wc_bit;
 };
 
+/* Macro for the currently active Window Port whose function
+   pointers have been loaded */
+#define WINDOWPORT(wn) \
+    (windowprocs.name && !strncmpi((wn), windowprocs.name, strlen((wn))))
+
 /* role selection by player_selection(); this ought to be in the core... */
 #define RS_NAME    0
 #define RS_ROLE    1