Comment 2 for bug 1982

It seems this is a problem with Python's bz2 module:

http://mail.python.org/pipermail/python-list/2005-August/296538.html

There's a workaround for this, which is to use

tarfile.open('', 'r|bz2', stream)

when the filename ends in '.bz2'. This means telling RosettaReadTarFile about the original filename when it is instantiated so that it can inspect it later.