[cairo] cairomm memory leaks (still)

[Austin Foxley]

As first noted in
http://lists.freedesktop.org/archives/cairo/2006-June/007112.html

Doing,

Glib::RefPtr<Gdk::Window> win = get_window();
Cairo::RefPtr<Cairo::Context> cr = win->create_cairo_context();

results in a memory leak (according to my valgrind runs).

I might be completely wrong (and please correct me) but I don't think
this is supposed to happen.

-Austin