[FIX] res_users: improve behavior when user record is locked during login
[FIX] res_users: improve behavior when user record is locked during login

Avoid logging an ugly and frightening traceback,
plus properly rollback the failed transaction before
continuing.
This is an extra fix for previous commit
rev. 4049 rev-id odo@openerp.com-20120213183207-45ptopqm0szritgx

akretion/openerp-server,akretion/openerp-server,akretion/openerp-server