Splitting module and libgames-support scores

[Robert Ancell <robert ancell gmail com>]

Hi,

The score system in libgames-support is now the last thing stopping us
from splitting the games into separate modules...

I think the best way forward is just to drop support for sharing
scores between users of the same system. I think this is OK because:
- I suspect the vast majority of the GNOME consumers don't use
multi-user systems so they never see any scores but their own.
- It uses setguid which is a bit questionably security wise and a pain
for distributors

Any opposition?
--Robert