[duim,gtk] There is no need for $null-gpointer.

This uses a binding for <gpointer> which no longer exists.
[duim,gtk] There is no gobject-glue library.

It has been folded into gobject.
[gtk] A real binding for Cairo.

This isn't from GIR files, but done via melange with significant
changes by hand to match the style of our other Gtk+ bindings.

It doesn't handle output parameters yet, but that can happen
incrementally as they are found.