Merged Indy exfat support with current make_bootable from source

Created originally on Bitbucket by 600dplus (scrax)

Was already merged in Bitbucket before import, marked as merged by the import user

Source changeset not longer availableat the time of import. Commit listwill look empty

also added compiled exfat_sum for osx and moved all to contrib folder check here: https://bitbucket.org/hudson/magic-lantern/commits/30e2d2414676841a6f3a6af3fe290e480bc09451#general-comments