FBOs are a GL 3.0 feature but enjoy nearly universal support via
extensions.
The newer ARB extension brings these features to GL 2.1 without needing
an ARB suffix.
The older EXT extensions *do* use a suffix. Since we don’t know which
is used until runtime, I added the suffix to all functions & enums.
Also updated the check to look for the FBO feature set instead of the
specific EXT extension.
b787341b09