- Add extN select-inum-for-allocation support, and use it to make recovery-time

- Add extN select-inum-for-allocation support, and use it to make recovery-time
  inode creation more deterministic.

- Test program and ioctl for the aforementioned wantedi support.

- Don't send MSG_LAST_REPLAY with the last-replayed lock.  Really.  I mean it
  this time.

- Some transno-reintegration CERROR removal, because the 9600bps conman on dev
  cramps the style of 300-transaction replays something fierce.

- Sync after every integrated transaction, so that we make forward progress
  in case of interrupted recovery.  (This will be replaced by the handle->h_sync
  fix foreshadowed in fsfilt_extN_commit.)

- Reuse reply_md.start instead of the likely-NULL rq_repmsg when resending reqs.

- Requests without transnos should be ERESTARTed _never_, not _always_.