support both old and new reader in the single source
* not pushing out fastmon file until this is implementing properly
* old-style reader merged with the new code. New parameter to control this
is numBuffers (untracked int32). 1 is the old method, 2 or more is n-buffering
with the new method
* files are now deleted after all CMSSW streams that previously processed that file
ask for an event after another file is open. the last file is deleted in the source destructor