This will allow sending requests even when no conflict occur. For example,
it can happen to avoid a deadlock on storage nodes (store again, no conflict
to resolve).
Also, call conflict resolution as soon as a conflict is known, to reduce
tpc_vote duration.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2594 71dcc9de-d417-0410-9af5-da40c76e7ee4