SF bug #1403349 solution for email 3.0; some MUAs use the 'file' parameter
name in the Content-Distribution header, so Message.get_filename() should fall
back to using that. Will port to the Python 2.5 trunk.
Also, bump the email package version to 3.0.1 for eventual release. Of
course, add a test case too.
XXX Need to update the documentation.