Purpose of this commit is to allow to attach moved messages from a thread
to a new parent. This allows notably to keep references if message
hierarchy is not kept as it is.
LINKS
Task ID-2083049
COM PR odoo/odoo#49129
ENT PR odoo/enterprise#9715
UPG PR odoo/upgrade#1883
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>