gsource: Make GSource->source_funcs const

This is the vtable pointer for the source which is usually held in
static storage.  For our internal sources it points at a vtable which
the user should really never be modifying.

Mark it const.

https://bugzilla.gnome.org/show_bug.cgi?id=686853

diff --git a/glib/gmain.h b/glib/gmain.h
index 90bc035..90ff11b 100644 (file)
--- a/glib/gmain.h
+++ b/glib/gmain.h
@@ -156,7 +156,7 @@ struct _GSource
   gpointer callback_data;
   GSourceCallbackFuncs *callback_funcs;
 
-  GSourceFuncs *source_funcs;
+  const GSourceFuncs *source_funcs;
   guint ref_count;
 
   GMainContext *context;