Richard B's patch to add WINDOWID support to pterm.

[originally from svn r2912]

unix/unix.h

@@ -47,6 +47,7 @@ GLOBAL void *logctx;
 /* Things pty.c needs from pterm.c */
 char *get_x_display(void *frontend);
 int font_dimension(void *frontend, int which);/* 0 for width, 1 for height */
+long get_windowid(void *frontend);
 
 /* Things uxstore.c needs from pterm.c */
 char *x_get_default(const char *key);