write-behind mtime workaround

[Brent A Nelson <brent@xxxxxxxxxxxx>]

Setting "option aggregate-size 0" does not eliminate the mtime glitch 
100%.  Copying /usr to an afr/unify glusterfs, I found that almost 
everything was okay, but a handful of files on one server had updated 
mtimes, and a different handful on the other server did, as well.

So, even with aggregation out of action, write-behind will still 
occasionally alter mtimes on a "cp -a".

Thanks,

Brent