HAMMER 60E/Many: Mirroring, bug fixes

HAMMER 60E/Many: Mirroring, bug fixes

* Work on the mirror_tid propagation code.  The code now retries on
  EDEADLK so propagation is guaranteed to reach the root.

* Get most of the mirror_write code working.

* Add PFS support for NFS exports.  Change fid_reserved to fid_ext and use
  it to store the localization parameter that selects the PFS.  This isn't
  well tested yet.

* BUGFIX: Fix a bug in vol0_last_tid updates.  Flush sequences might
  not always update the field, creating issues with mirroring and snapshots.

* BUGFIX: Properly update the volume header CRC.

* CLEANUP: Fix some obj_id's that were u_int64_t's. They should be int64_t's.

* CLEANUP: #if 0 out unused code, remove other bits of unused code.