CCEffectStack - Make stitchEffects a class method

There's no reason for it to be an instance method so in the interest of compartmentalization
I'm changing it.
CCEffectStack - Fix a bug in stitching of multi-pass effects like bloom and blur

The passes of these effects would be improperly collapsed into a single pass which
cannot be done since they must maintain their multi-pass implementation. Fix this
and add a test that exercises this use case.
CCEffectsTest - More sprites in the performance test plus stacks of stacks
Merge pull request #989 from thayerandrews/develop

CCEffects - Stacking bug fixes plus test additions