[Reviewer Matt] Plug leaks in Sprout

Excuse the vegetable metaphors.  Can you review asap - hopefully the changes are pretty self-explanatory.

I've tested using your valgrind stress run and run UTs.  The memcached leaks have complete gone, and it looks like the transaction leaks have reduced enormously, but there may still be some leakage - but I'd like to get this much released asap.

Mike