The window needs to catch ClientMessage events for one specific window, but
XNextEvent() catches everything, and XWindowEvent doesn't catch ClientMessage,
so we need predicate procedure and XIfEvent() here.
Fixes Bugzilla #2980.
An existing hint lets apps that don't need the timer resolution changed avoid
this, to save battery, etc, but this fixes several problems in timing, audio
callbacks not firing fast enough, etc.
Fixes Bugzilla #2944.