Merged completed be.email-bugs branch.

Highlights:
  * import-xml now works as advertized in its longhelp string
  * new methods Bug.merge() and Comment.merge()
  * comment.list_to_root() is now Bug.add_comments()
  * BugDir.list_uuids() is now BugDir.uuids()
  * Bug.from_xml() now imports comments :p
  * test.py uses unittest.TestSuite 'suite' in becommands, if present.