GL_EXT_stencil_clear_tag
http://www.opengl.org/registry/specs/gl/EXT/stencil_clear_tag.txt
GL_EXT_stencil_clear_tag
	GL_STENCIL_TAG_BITS_EXT 0x88F2
	GL_STENCIL_CLEAR_TAG_VALUE_EXT 0x88F3