weak_pointer_location parameter to g_object_add_weak_pointer

[Darin Adler <darin bentspoon com>]

The weak_pointer_location parameter to g_object_add_weak_pointer and
g_object_remove_weak_pointer is gpointer *, but it should really be
gpointer, or else anyone who uses this has to use a cast unless they store
the pointer in a gpointer rather than a GtkWidget * or whatever. I seem to
recall some discussion of this in the past.

Is it too late to fix this? Note that relaxing the parameter type to
gpointer would be unlikely to break any code, unless it involved a pointer
to the g_object_add_weak_pointer function itself.

    -- Darin