It was actually used to track individual answerStoreTransaction, and there
is no need to track them individually.
Instead, just set txn_voted to True before returning, so it really means
that tpc_vote ended successfully.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2518 71dcc9de-d417-0410-9af5-da40c76e7ee4