Comment 1 for bug 973747

This has already been fixed in precise:

update-manager (1:0.156.2) precise; urgency=low

  [ Michael Vogt ]
  * DistUpgrade/removal_blacklist.cfg:
    - add unity, unity-2d

  [ Brian Murray ]
  * debian/source_update-manager.py: use attach_file for dist-upgrade log
    files rather than attach_root_command_outputs resolving the double gzipped
    apt clone attachment issue