Fix a rounding bug with Catalyst drivers, at least on Windows with
ATI/AMD 4800-series cards.  Make all affected lines reference the
same constant, and make a few related variable names more consistent.
crt-royale: Add notes about Retroarch version requirements, because
the latest official release (1.0.0.2) does not support a lot of
semi-required features.
Merge pull request #31 from TroggleMonkey/master

Fix a rounding bug with Catalyst drivers, at least on Windows with