GL_EXT_subtexture
http://www.opengl.org/registry/specs/EXT/subtexture.txt
	void glTexSubImage1DEXT (GLenum target, GLint level, GLint xoffset, GLsizei width, GLenum format, GLenum type, const void* pixels)
	void glTexSubImage2DEXT (GLenum target, GLint level, GLint xoffset, GLint yoffset, GLsizei width, GLsizei height, GLenum format, GLenum type, const void* pixels)
	void glTexSubImage3DEXT (GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint zoffset, GLsizei width, GLsizei height, GLsizei depth, GLenum format, GLenum type, const void* pixels)
