Shashlik out of time pileup mitigation

Multifit for ecal pulse shapes backport from 7_something, and PF pileup mitigation changes.  Includes #5845.

@bachtis, I had to add a change to class checksums
@lgray, @bendavid, FYI
Good point.  I assumed it either inherited from a changed class or had one as a member.  Looking closer that doesn't appear to be the case though.