alternative mode is computed when browsing the parts, not from
the message content type.
Added tests.
Also added some notification_email_send to none to avoid sending
emails in demo/data/update.
bzr revid: tde@openerp.com-20130823120611-0n4ull3c8gvwug2u
Before trying to find possible routes, check that the incoming email's
message_id is not already present in mail.message table.
If it is the case, return False.
Parsing of the message has been moved before routing, to avoid looking
for routes for emails we will discard.
Tests have been added and updated.
bzr revid: tde@openerp.com-20130322124809-ven2p5kxpqfjqxb5
Thibault Delavallée