Avoid error with imaplib quoting

Testing against our imap server, I got the following exception.

Traceback (most recent call last):
  File "./bot.py", line 765, in <module>
    main(fp)
  File "./bot.py", line 729, in main
    fetcher.delete(message.message_id)
  File "./bot.py", line 319, in delete
    self.imap_mail.uid('store', message_id, '+FLAGS', r'\\Deleted')
  File "/usr/lib/python2.7/imaplib.py", line 760, in uid
    typ, dat = self._simple_command(name, command, *args)
  File "/usr/lib/python2.7/imaplib.py", line 1070, in _simple_command
    return self._command_complete(name, self._command(name, *args))
  File "/usr/lib/python2.7/imaplib.py", line 905, in _command_complete
    raise self.error('%s command error: %s %s' % (name, typ, data))
imaplib.error: UID command error: BAD ['Error in IMAP command UID STORE: Flags list contains non-atoms.']

Fixed by adding parens to the string, as recommended here:
http://docs.python.org/2/library/imaplib.html#imap4-objects