Make the local tests use "normal" unittest conventions.

Tim pointed out that loadEx is supposed to return a 3-tuple.  This is related to collector 1828 which was already marked as resolved.

The caller can't deal with using current data from loadBefore, so having an "end_tid" of None is useless.

Allow tempstorage to participate in MVCC.  Also fix minor bug where conflict cache could be poisoned by a transaction that failed after store was called.