Cocoa: Fix compilation on Mac OS X v10.4 and earlier

Cocoa: Fix compilation on Mac OS X v10.4 and earlier

NSView's enterFullScreenMode:withOptions: and
exitFullScreenModeWithOptions: are available on v10.5
and later only. Undefined methods raise warnings and
undefined constants result in errors.

Reported by Ryan Schmidt.

While at it, avoid a warning on v10.3.9,
where MAC_OS_X_VERSION_10_4 is not defined.

Spotted by John Arbuckle.

Fix associated comments.

Signed-off-by: Andreas Färber <andreas.faerber@web.de>
Cc: John Arbuckle <programmingkidx@gmail.com>
Cc: Ryan Schmidt <qemu-2009@ryandesign.com>
Cc: Mike Kronenberg <mike.kronenberg@kronenberg.org>
Signed-off-by: malc <av1474@comtv.ru>