foreign-cairo: Fix cairo marshalling not using the foreign converters in some cases. Fixes #260

In case the first cairo marshall happens through the GType converters we wont have loaded the cairo foreign module yet and wont have registered the right converters. This results in the non-foreign version getting passed on which isn't accepted by all other marshalling paths which use the foreign module.

Try importing the cairo foreign module at gi import type instead so the gtype converters are registered.