[IMP] [WIP] mail: Set an OpenERP alias as the bounce address.

Attempts to fix issue #3347.

This makes OpenERP 7.0 issue a SMTP MAIL FROM command with an address it "owns".
The warning will be logged for every outgoing email when there is no `mail.catchall.alias` nor  `mail.catchall.domain` defined, while the most likely outcome is that they will be delivered just fine.
I don't think it's quite necessary. If you insist, at least put it in DEBUG level ;-)