#11 Increase efficiency of flood search

[Travis Brown]

Currently the flood search is n^3 because we don't keep track of whether we've seen it.

Keeping track will require some memory, but will make the flood search cost only n^2 in the case where not too many floods happen at once.

To do this keep a small (1024-4096 entry) LRU and check that before forwarding. Also add a unique identifier.