updated window_procs

Add a non-string identifier to window_procs for use in runtime
identification of the current window port being used.

Use a macro WPID to add the identification at the top of the
various existing window_procs declarations. It expands to the
existing text string, as well as the newly added field wp_id
with a wp_ identifier.

For example, WPID(tty) expands to: "tty", wp_tty

The generated wp_tty must be present in the wp_ids enum at
the top of include/winprocs.h.

The WINDOWPORT(x) macro has been updated to expand to a simple
value comparison (port.wp_id == wp_x), instead of a
string comparison.

win/tty/wintty.c

@@ -98,7 +98,7 @@ extern void msmsg(const char *, ...);
 
 /* Interface definition, for windows.c */
 struct window_procs tty_procs = {
-    "tty",
+    WPID(tty),
     (0
 #ifdef TTY_PERM_INVENT
      | WC_PERM_INVENT