Merge pull request #909 from thayerandrews/develop

CCEffects - Various bug fixes, cleanup, and tweaks based on feedback
CCEffectStack - Match convenience constructor flavors to those in CCActionSequence

There is now an NSArray* version and a nil-terminated list version. This also introduces a
convenience va_list initializer but that's internal only.
CCEffectBloom - Fix intensity math

The intensity value needs to multiply all instances of the source term in the screen
blending equation. Otherwise, even when intensity is zero, the source term is still
contributing to the final result which is not what we want.
Fixing an old warning.
CCEffectBloom - Fix threshold math

When applying the luminance threshold, don't check the luminance of the blurred result pixel and instead
check the luminance of the inputs to the blur operation. If the luminance of an input falls below the
threshold just use black as the input instead. Because the threshold happens before the blur, the
boundaries of the thresholded areas are still nicely blurred. Doing the threshold after the blur results
in hard boundaries that don't achieve the effect we want.

Note that the addition of the luminance calculation and the step() function does have a negative
performance impact. We're going with this implementation for now but this is an argument for
supporting multiple shaders / implementations per-effect. With multiple implementations, we could
select one that does not pay the performance penalty for the threshold check if it's not needed.
CCEffectsTest - Add effects with varying luminance thresholds to the bloom test
Merge remote-tracking branch 'upstream/develop' into develop