Experimental SUJ feature; cache synchronization

[Jeff Roberson]

Hello,

As of rev 242815 current has a feature to issue a synchronize cache 
command to the drive in between journal records and the metadata they 
modify.  This should make SUJ more safe in the face of power failure. 
This should be considered experimental at this phase.  If you wish to try 
it you may enable it at any time with:

sysctl debug.softdep.flushcache=1

Thanks,
Jeff