Merge pull request #873 from thayerandrews/develop

CCEffects - Designated initializer cleanup, fix nil environment in refraction
CCEffectRefraction - Address feedback from Viktor

- Fix the blend of the main texture and the refracted environment texture. It was a multiply, now it's a
  premultiplied alpha blend.
- If the refracted texture coordinates would index outside the environment texture, just return the main
  texture.
CCEffectRefraction - Crash fix when sprite texture / sprite frame is nil
CCSprite - Set the sprite's texture rect from the normal map if there is no main texture.
Merge remote-tracking branch 'upstream/develop' into develop