* 12to11.man: Document new protocol.
* compositor.h (enum _RenderMode): Add RenderModeVsyncAsync.
* picture_renderer.c (SwapBackBuffers, PresentToWindow)
(NotifyMsc): Handle new render mode.
* sync_source.c (GetWantedSynchronizationType): Use presentation
if the mode is VsyncAsync.
(NoteFrame): Set the vsync presentation mode to
RenderModeVsyncAsync.