o) Go back to a lookahead decoder so we don't have to do an ASK/LEARN at a time,
   that will be really painful on long, slow links.
o) Add a PAUSE/RESUME mechanism so that we don't have, say, more than 1MB of data
   queued up during an ASK/LEARN session?  PAUSE when we send an ASK with more
   than 1MB or data or get more than 1MB of data with an ASK outstanding, and then
   send a RESUME once we get <1MB of data outstanding?
o) Use a 16-bit window counter rather than an 8-bit one so we have an 8MB window
   rather than a 32KB one.
   XXX Preliminary tests show this to be a big throughput hit.  Need to check
       whether the gains are worth it.
o) Don't let a peer claim to have our UUID?
o) Permanent storage.
o) Decide whether to keep a std::set (or something fancier) of hashes associated
   with each UUID (i.e. ones we have sent to them).  We could even make it a
   set of <UUID,UUID,hash> so that we can distribute updates like routing
   tables.
o) Do lookups in the peer's dictionary and ours at the same time.
o) Put a generation number in the hashes so that if the remote side recycles a
   hash, we can do something about it.