"Recursive" option for KVS directory gets

[trws]

I'm starting to run into a number of places where it would be beneficial to condense the read of an entire tree into a single request. This would probably need to either have a size limit, or return the results in chunks rather than be left completely unbounded, but providing the lookup-equivalent of a transaction would be pretty helpful for performance in some of my code.

[garlick]

Closing old issue. Reopen if this is still compelling given where we are now.