This fixes a bug where, if current time was more than a minute before
_last_tid, returned TID would be decreasing because gmt is reused in
collision resolution code instead of reading _last_tid's date.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2469 71dcc9de-d417-0410-9af5-da40c76e7ee4