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
Got rid of my ~/.rootlogon.C file and now it works fine.  The only entries were

    gSystem->Load("libFWCoreFWLite.so");
    AutoLibraryLoader::enable();

@davidlange6 @Dr15Jones is this supposed to interfere with the build?