OID 0 is a very valid oid. It's often used for the most important object of
the database: the root object. Using 0xffffffffffffffff leaves some space.

TID 0 is a very valid tid, for transactions back in unix year 0... or
ZODB tests. Using 0xffffffffffffffff leaves some space.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@1977 71dcc9de-d417-0410-9af5-da40c76e7ee4