Merge the 2571 double-buffering stuff over and delete the 2571 branch.  Double buffering of the file merge is complete.  Fixes #2571. close[t:2571]
{{{
svn merge -r 20199:20206 https://svn.tokutek.com/tokudb/toku/tokudb.2571
}}}
.


git-svn-id: file:///svn/toku/tokudb@20208 c7de825b-a66e-492c-adef-691d508d4ae1