Fixed mail upgradestep `to3401`, when it's run multipletimes.

With the current implementation, the new behavior gets doubled in the fti behaviors list
and makes some troubles when transporting to another clients (see `opengever.ogds.base.transporter`).
Fixed mail upgradestep `to3402`, when it's run multipletimes.

With the current implementation, the classification gets doubled in the fti behaviors list
and makes some troubles when transporting to another clients (see `opengever.ogds.base.transporter`).
Merge pull request #678 from 4teamwork/pg_fix_mail_upgradestep

Fix mail upgradesteps (to3401 and to3402)