Implement monitor refresh rate synchronization on X

Implement monitor refresh rate synchronization on X

* src/xfns.c (x_set_parent_frame, Fx_create_frame): Disable
vsync on child and embedded frames.
* src/xmenu.c (x_menu_show): Fix XMenu position calculation in
child frames.

* src/xterm.c (x_sync_is_frame_drawn_event)
(x_sync_wait_for_frame_drawn_event): New functions.
(x_sync_update_begin): Wait for frame to be drawn if not double
buffered.
(x_sync_update_finish): Set FRAME_X_WAITING_FOR_DRAW (f).
(show_back_buffer): Wait for frame to be drawn before flipping
buffers.
(XTframe_up_to_date): Set FRAME_X_WAITING_FOR_DRAW if bumped.
(handle_one_xevent): Handle frame drawn events.

* src/xterm.h (struct x_output): New fields for frame dirtyness
and vsync.