[FIX] base_calendar: meetings email notification recipients

Reminder emails are generated based on the list of attendees.
The email_to field used to be a string with a list of emails separated by spaces
while the comma is the valid separator (RFC2822).
Fixes #3933 #3784 #2033
[FIX] account: chart of account opening period selection

If a special period is present, it must be selected fist
Fixes #3946
[IMP] ir_mail_server: Set an OpenERP alias as the bounce address.

Fixes issue #3347.