nowdays .tar.gz and .tar.bz2 files are recognized as
application/x-bzip and application/x-gzip respectively.
also added application/x-gzip-compressed-tar because
application/x-bzip-compressed-tar is in the list and I
think that's a legacy one but should not hurt.
Signed-off-by: Ivailo Monev <xakepa10@gmail.com>