If the value evaluates to False, don't update preindex.
If the value is a string, update preindex entry for given oid.
Otherwise, iterate over it, it must contain (oid, serial) tuples.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@1755 71dcc9de-d417-0410-9af5-da40c76e7ee4