GL_EXT_polygon_offset
http://oss.sgi.com/projects/ogl-sample/registry/EXT/polygon_offset.txt
	GL_POLYGON_OFFSET_EXT 0x8037
	GL_POLYGON_OFFSET_FACTOR_EXT 0x8038
	GL_POLYGON_OFFSET_BIAS_EXT 0x8039
	void glPolygonOffsetEXT (GLfloat factor, GLfloat bias)