Added caching of X11 NULL atom.
Fixed missing ICCCM protocol message checks.
Added glfwPostEmptyEvent.
Added test for posting of empty event.
Video mode detection cleanup.
Fixed invalid video mode being restored.
Added window creation intent printing.
Added missing detection of invalid flags.
Formatting.
Only set the monitor callback once.
Replace CGDisplayIOServicePort with a workaround

This could be cleaned up and refined a bit by comparing more display
attributes when available, but it gets the job done.

Closes #192.
Cleanup of CGDisplayIOServicePort replacement.
Fixed leak of display name.
Formatting.
Fixed glfwDestroyWindow not flushing the output buffer.