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.

gtk/gtkdialog.c

@@ -206,7 +206,7 @@ gtk_dialog_class_init (GtkDialogClass *class)
 
   binding_set = gtk_binding_set_by_class (class);
   
-  gtk_binding_entry_add_signal (binding_set, GDK_Escape, 0, "close", 0);
+  gtk_binding_entry_add_signal (binding_set, GDK_KEY_Escape, 0, "close", 0);
 }
 
 static void