Some Mac / __APPLE___ cleanups:

Some Mac / __APPLE___ cleanups:

    - remove the OSX_BUNDLE crap *I* introduced years ago - we're always a a bun
dle on Mac now.

    - fix up the default fg-root on Mac to be FlightGear.app/Contents/Resources/
data - i.e the location used by the macflightgear.org distro, and indeed the obv
ious 'correct' location. Not sure why I didn't use that in the first place, back
 in the day.

    - remove the CPSForegroundEnable hack. For one thing, we're a bundle and don
't need it, and for another, osgViewer on Mac does the same logic using a newer,
 public API rather than a hack into the OS.

    - remove the strange logic for doing fgOSInit 'early' (in bootstrap rather t
han main) when running from the command line on Mac; again this is obsolete, and
 no one seems to know why it was ever necessary. I guess it was an interaction w
ith SDL when running without a bundle.

    - (not Mac related) remove obsolete code bracketed by ENABLE_PLIB_JOYSTICK a
nd USE_GLIDE (neither of which are ever set, even from config.h that I can see)
in main.cxx