On Haiku, sync a frames's connection to the app sever after raising

On Haiku, sync a frames's connection to the app sever after raising

* src/haiku_support.h: (BWindow_sync)
* src/haiku_support.cc (BWindow_sync): New function.
* src/haikuterm.c (haiku_frame_raise_lower): Synchronize window
after raising it to avoid situations where raising windows is
done out-of-order, such as when ediff raises a frame.