HAMMER 18/many: Stabilization pass

HAMMER 18/many: Stabilization pass

* Properly flag the inode when dirty buffer cache buffers are present so
  fsync syncs them.  Fixes a umount panic.

* Fix A-list bugs introduced when I added the '10' bit code to record
  an all-allocated/initialized state vs '00' (all-allocated uninitialized).

* Fix an A-list bug in *alloc_rev.  A comparison was off and could result
  in a near full A-list from incorrectly believing it was completely full.

* When generating a spike also allocate a spike record for the recovery code
  to find.

* Generate the initial free blocks for a hammer buffer via its cluster A-list
  instead of directly so the cluster A-list's meta-data is properly
  synchronized.