HAMMER 25/many: get fsx (filesystem test) working, cleanup pass

HAMMER 25/many: get fsx (filesystem test) working, cleanup pass

* Fix buffer alignment in the write strategy code.  Assert buffer alignment
  in hammer_ip_sync_data().

* Finish implementing file truncation.  There's probably still an edge case
  or two related to B_CACHE on terminal filesystem buffers when expanding
  a file.

* Pass VCHR vnodes through to fsync so the inode data syncs properly.  It
  was previously only syncing on umount or OS flushes.

* Change a bunch of debugging kprintf's to only print if a debug variable is
  set.  Reduce the debugging output considerably.

* Test FSX using both a full historical mount and a nohistory mount.