Fixed wording issue pointed out by Gregg Tavares in packing restrictions for uniforms and varyings.
Merge pull request #175 from kenrussell/packing

Fixed wording issue pointed out by Gregg Tavares in packing restrictions...
Per resolution of WebGL WG, and after discussion with OpenGL ES WG, made certain FBO attachment combinations mandatory, and tested this requirement in the framebuffer-object-attachment test.
Removed unused variable.
Merge pull request #176 from kenrussell/fboattachments

Per resolution of WebGL WG, and after discussion with OpenGL ES WG, made...