Better Mac Filesystem Handling (QDir)

At the moment, when using e.g the dirview example, Mac applications show up in the list as directories with .app extensions. Root directories that are normally hidden in the Finder also show up (eg. usr, bin, etc). These could manually be filtered out, but it seems like something that should be built into the QDir object. Users could inadvertently drop files into application bundles or these hidden Finder directories and be unable to find them again.

Perhaps a new filter, QDir::MacFinder, could be added. This would cause QDir to use the appropriate Carbon calls instead of the UNIX/
POSIX filesystem calls.

The dirview example app demonstrates this problem.