GL_INTEL_texture_scissor
http://www.opengl.org/registry/specs/INTEL/texture_scissor.txt
	void glTexScissorFuncINTEL (GLenum target, GLenum lfunc, GLenum hfunc)
	void glTexScissorINTEL (GLenum target, GLclampf tlow, GLclampf thigh)
