GL_EXT_copy_texture
http://oss.sgi.com/projects/ogl-sample/registry/EXT/copy_texture.txt
	void glCopyTexImage1DEXT (GLenum target, GLint level, GLenum internalformat, GLint x, GLint y, GLsizei width, GLint border)
	void glCopyTexImage2DEXT (GLenum target, GLint level, GLenum internalformat, GLint x, GLint y, GLsizei width, GLsizei height, GLint border)
	void glCopyTexSubImage1DEXT (GLenum target, GLint level, GLint xoffset, GLint x, GLint y, GLsizei width)
	void glCopyTexSubImage2DEXT (GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint x, GLint y, GLsizei width, GLsizei height)
	void glCopyTexSubImage3DEXT (GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint zoffset, GLint x, GLint y, GLsizei width, GLsizei height)
