Fixes to texture sizing and cocos2d state management.

Fix incorrect setting of CC3GLTextureCube isFlippedVertically property. Fix texture
scaling for NPOT textures. Move semantic kCC3SemanticIsUsingLighting to node scope.
When moving from 3D to 2D, reset state of only those attribute arrays used by cocos2d.
Upgrade PowerVR library to version 3.1.
Add PVR cube-map support.

Add PVR cube-map support. Load PVR files using PVRT library.
Ensure both 2D & cube textures disabled & unbound for unused tex units.
Ensure tex unit 0 is active when leaving 3D.