GDK: Prefix key names with KEY_

The keysyms create a lot of potential namespace conflicts for
C, and are especially problematic for introspection, where we take
constants into the namespace, so GDK_Display conflicts with GdkDisplay.

For C application compatiblity, add gdkkeysyms-compat.h which uses
the old names.

Just one user in GTK+ continues to use gdkkeysyms-compat.h, which is
the gtkimcontextsimple.c, since porting that requires porting more
custom Perl code.

docs/tools/widgets.c

@@ -270,7 +270,7 @@ create_accel_label (void)
 
   info = new_widget_info ("accel-label", box, SMALL);
 
-  gtk_widget_add_accelerator (button, "activate", accel_group, GDK_Q, GDK_CONTROL_MASK,
+  gtk_widget_add_accelerator (button, "activate", accel_group, GDK_KEY_Q, GDK_CONTROL_MASK,
 			      GTK_ACCEL_VISIBLE | GTK_ACCEL_LOCKED);
 
   return info;