Such function is provided when message is queued for send when an answer
is expected, and is called when the answer is not arrived after expiration
of the timeout delay. Depending on the return value of this callback, the
timeout is ignored (True) or passed through (False).

Also, move code to refresh next timeout value to a separate function, for
reusability.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2106 71dcc9de-d417-0410-9af5-da40c76e7ee4