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.