Fix color and depth buffer cache for windows that change size.  Fix documentation referring to "singleton" buffer manager instead of per-context.
Fix color and depth buffer cache for windows that change size.  Fix
documentation referring to "singleton" buffer manager instead of per-context.

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extra : convert_revision : svn%3A14d46d22-621c-0410-bb3d-6f67920f7d95/trunk%402144

infowantstobeseen/pyglet-darwincore,infowantstobeseen/pyglet-darwincore,infowantstobeseen/pyglet-darwincore,infowantstobeseen/pyglet-darwincore,infowantstobeseen/pyglet-darwincore