[IMP] mail_alias: added reference to the parent record.

[IMP] mail_alias: added reference to the parent record.
The parent record is the record that holds the alias. It is different
from the record updated or created using the alias. For example
projects have aliases whose parent is the given projet, and that creates
new task inside the project.
Updated alias creation and management accordingly.
This ownership concept is used to compute the 'followers' contact
settings of aliases.

bzr revid: tde@openerp.com-20130516164207-1zr0q6abw6a34ndf