Added 'remove' command to remove bugs. Use __desc__ for command help.

Added 'remove' command to remove bugs.  Use __desc__ for command help.

Using the __desc__ reduces documentation duplication.  It's also better
than using __doc__, because __doc__ could (should?) be more than one-line
long, and we just want a short description to jog our memories in the
complete command list.

Also moved unique_name from cmdutil.py to names.py to avoid the
  bug->cmdutil->bugdir->bug
cyclic include.