Fix txns from asynchronous pubsub

txns received from pubsub when not inside the txn middleware now work
correctly.

I fixed the code the buffered them, and added serialCleanup() calls to
flush the buffer.
This seems to work well, and fixes #110

To make the fix work, all pubsub events are now published asynchronously.  (including the in-memory adapter)  
This should not break anything.