GL_APPLE_flush_buffer_range
http://www.opengl.org/registry/specs/APPLE/flush_buffer_range.txt
	GL_BUFFER_SERIALIZED_MODIFY_APPLE 0x8A12
	GL_BUFFER_FLUSHING_UNMAP_APPLE 0x8A13
	void glBufferParameteriAPPLE (GLenum target, GLenum pname, GLint param)
	void glFlushMappedBufferRangeAPPLE (GLenum target, GLintptr offset, GLsizeiptr size)
