VMM/Account: some modifications and small improvements in class Account. - replaced the tid by a Transport instance - check mailbox format dependencies in _repare() - reset all attributes when the Account was deleted - don't select information, we have already, from the db - added __nonzero__() method

# -*- coding: UTF-8 -*-
# Copyright (c) 2007 - 2010, Pascal Volk
# See COPYING for distribution information.

MISSING_ARGS = 1
UNKNOWN_COMMAND = 2
USER_INTERRUPT = 3