The terminal window can now indicate that PuTTY is busy in various ways, by

changing its mouse pointer. Currently this is only used in the (slightly-
arbitrarily-defined) "heavy" bits of SSH-2 key exchange. We override pointer
hiding while PuTTY is busy, but preserve pointer-hiding state.

Not yet implemented on the Mac.

Also switch to frobbing window-class cursor in Windows rather than relying on
SetCursor().

[originally from svn r5303]

unix/uxcons.c

@@ -31,6 +31,10 @@ void cleanup_exit(int code)
     exit(code);
 }
 
+void set_busy_status(void *frontend, int status)
+{
+}
+
 void update_specials_menu(void *frontend)
 {
 }