[CMake] Bundle Generator conflicts with MACOSX_BUNDLE

[Mike Arthur]

The subject says it all, the CPACK Bundle Generator conflicts with 
MACOSX_BUNDLE and produces two nested Bundles. This should probably be checked 
for and/or documented because I assumed the two were related and wasted a fair 
bit of time working out that they weren't.

Nice work though on both counts!

-- 
Cheers,
Mike Arthur
http://mikearthur.co.uk/