VertexShaderManager: Add stereoscopy options to swap the left and right eye.
OGL: Add Top-and-Bottom stereoscopy mode.
ProgramShaderCache: Don't call glAttachShader if no geometry shader was compiled.
TextureCache: Use interface blocks in shader programs.

And fix an invalid cast while we're at it.
OGL: Also redefine glFramebufferTexture on OpenGL ES.