AppendEntries mostly working
64-bit entry numbers in some calls
Use motes instead of u2_raty
u2_sist structure
Various minor fixes

Also remove the checkpoint notification for now.
Start u2_reck entry numbers from 0
Remove did
Various raft cleanups

Including unconditional u2_lo_lead, relying on lead to differentiate
batch vs. interactive mode.
Trivial ames cleanup
Split term and sist initialization

Also remove the log conversion code and make ular sequence numbers
64-bit.
Shuffle sist around
64-bit in raft push
Send heartbeats immediately on election
Send apen rather than beat

Now apen falls back to beat if we don't have anything to send.

Also made u2_sist_rent return n entries at a time, and made it slightly
more robust.
New restore in terms of song
Raft mostly working

Testing locally with an election timeout of 150-300s.
Clean up boot output slightly
Only call u2_sist_song in single-instance mode

Upside: prevents our commitIndex from going crazy.

Downside: new events get played back against a bogus core until we're
caught up, probably necessitating some further logic in _raft_push.
Minor raft cleanup
More verbose failure reporting on apen