Give running Chimera the focus when user clicks on Dock icon or tries
to relaunch Chimera.
register_apple_event_handler
register_apple_event_handler ()
Register handler for Apple events, like data file being dropped on Chimera
icon, or click on Chimera icon to bring application window to top.
is_display_accessible
is_display_accessible ()
If user is not logged in on console some Mac calls that need access
to the screen cause an abort() on 10.4.11 but not on 10.5.2. This
routine allows checking for access so that abort() can be avoided.