GL_EXT_blend_minmax
http://oss.sgi.com/projects/ogl-sample/registry/EXT/blend_minmax.txt
	GL_FUNC_ADD_EXT 0x8006
	GL_MIN_EXT 0x8007
	GL_MAX_EXT 0x8008
	GL_BLEND_EQUATION_EXT 0x8009
	void glBlendEquationEXT (GLenum mode)