Emit a flush after the swapbuffers blit, so contents end up on the screen.

Emit a flush after the swapbuffers blit, so contents end up on the screen.

Otherwise, since the MI_FLUSH at the end of every batch had been removed,
non-automatic-flushing chips (965) wouldn't get flushed and apps with static
rendering would get partial screen contents until the server's blockhandler
flush kicked in.