libffi4 to libffi5

["Jason D. Clinton" <me jasonclinton com>]

It appears that between 2.22.0 and 2.22.1, I lost the ability to build
Gnome Games until I ripped out the previously working libffi4-dev and
replaced it with libffi5-dev. External dependencies being what they
are, this is a bit disconcerting. I suspect that something in the
Python toolchain is to blame; not our module. Anyone have any ideas?

Don't want to get caught with our pants down when someone comes asking...