The Mac driver captures the displays when the program changes the display
mode.  If the user types Command-Tab to switch away, it resets the displays
to their original modes and releases them.  However, if they switched back,
it didn't restore the mode to what the program had set, so the program often
showed the game window in a corner of the screen with the top behind the Mac
menu bar.

Also standardize on the 'Usage:' prefix for usage messages.

winmm: Fix two error messages to not point users to a MIDI Mapper configuration applet we don't have.