foreign: Register cairo.Path and cairo.FontOptions foreign structs

They are rarely used, but they are used at least by Gdk, PangoCairo and
Clutter.

clutter.Path is not used by any API that the test suite uses, so leave that
without a test for now.

https://bugzilla.gnome.org/show_bug.cgi?id=677388



Signed-off-by: Martin Pitt <martinpitt@gnome.org>