Merge pull request #6693 from MSOpenTech/wp8-v3-fix2

Fixes for WP8 V3 build recently broken by recent commits
GLProgramState fixes

It is possible to submit to the Renderer a Sprite with custom uniforms
(although it won't be batched).
It is possible to use a custom shader + uniforms on Sprite with
subclassing Sprite
Merge pull request #6694 from ricardoquesada/shader_fixes

GLProgramState fixes