Pierre-Yves David <pierre-yves.david@fb.com> [Fri, 17 Oct 2014 21:57:32 -0700] rev 23357
transaction: have _generatefile return a boolean
The function returns True if any files were generated. This will be
used to know if any pending files have been written.
transaction: allow generating files with a suffix
This will allow us to generate temporary pending files. Files
generated with a suffix are assumed temporary and will be cleaned up
at the end of the transaction.