CommonStoreTransaction object has no attribute enqueue

[David Austin]

calendarserver crashes at startup - using the file store... have user_xattr
enabled (though this is a VPS, so maybe not effective?)

2015-12-28 14:20:00+1100 [-] Unhandled Error
        Traceback (most recent call last):
          File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1099, in _inlineCallbacks
            result = g.send(result)
          File "/usr/lib/python2.7/dist-packages/twext/enterprise/queue.py", line 1279, in workCheck
            txn, (itemType.notBefore < tooLate))
          File "/usr/lib/python2.7/dist-packages/twext/enterprise/dal/record.py", line 331, in query
            Where=expr, **kw), None)
          File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1237, in unwindGenerator
            return _inlineCallbacks(None, gen, Deferred())
        --- <exception caught here> ---
          File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1099, in _inlineCallbacks
            result = g.send(result)
          File "/usr/lib/python2.7/dist-packages/twext/enterprise/dal/record.py", line 365, in _rowsFromQuery
            rows = yield qry.on(transaction, raiseOnZeroRowCount=rozrc)
          File "/usr/lib/python2.7/dist-packages/twext/enterprise/dal/syntax.py", line 213, in on
            queryGenerator = QueryGenerator(txn.dialect, self._paramstyles[txn.paramstyle]())
        exceptions.AttributeError: 'CommonStoreTransaction' object has no attribute 'dialect'