Event mixing with a list of input files.
I was running an event mixing test with two input files, the first containing 505 events and the second containing 513 events. My test job mixes in exactly 10 events from the mixing file per primary event. I asked for 60 primary events. The first 50 primary events take the first 500 events from the first file ( events 0 through 499). The 51st primary event contains events 500 through 509 from the secondary file. The mixing template throws on the 52nd event because it reaches the end of the second file.
Fixes for issue #1921.
MixHelper: nEventsRead_ must be reset upon file change.
RootBranchInfoList: reset() method did not clear data_; more safety.