 - Implement BIO_FLUSH support around journal entries.  This will not 100%    solve power loss problems with dishonest write caches.  However, it    should improve the situation and force a full fsck when it is unable    to resolve with the journal.  - Resolve a case where the journal could wrap in an unsafe way causing    us to prematurely lose journal entries in very specific scenarios.
 - Implement BIO_FLUSH support around journal entries.  This will not 100%
   solve power loss problems with dishonest write caches.  However, it
   should improve the situation and force a full fsck when it is unable
   to resolve with the journal.
 - Resolve a case where the journal could wrap in an unsafe way causing
   us to prematurely lose journal entries in very specific scenarios.

Discussed with:	mckusick
MFC after:	1 month

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase