Save dset info for empty source configs to FileInterface object.
Set read to 1 for successful file-based jobs.
Adding cmssw config for merging.
Moving retry function to base JobProvider class, so that both MergeJobProvider and cmssw JobProviders can use it.
Update parrot_run, etc, at each JobProvider initialization, instead of only during sandbox creation; also, move it to the base class, so that MergeProviders can use it, too.
Fix FileInterface for non-cmssw jobs.
Adding new JobitStore methods for merging.