Add informative exception for hash collision

[wmtan]

Fedor Ratnikov ran a reco job that asserted because two different branches had the same 32 bit hash for a branch ID. Unfortunately, we cannot easily fix the hash collision issue, but at least we can issue a clear and informative exception when this occurs, instead of a cryptic assert.

[cmsbuild]

A new Pull Request was created by @wmtan for CMSSW_7_5_X.

Add informative exception for hash collision

It involves the following packages:

FWCore/Framework

@cmsbuild, @Dr15Jones can you please review it and eventually sign? Thanks.
@Martin-Grunewald, @wddgit this is something you requested to watch as well.
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@Degano you are the release manager for this.
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[cmsbuild]

Pull request #9647 was updated. @cmsbuild, @Dr15Jones can you please check and sign again.

[Dr15Jones]

please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: 2dff79f
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-9647/10365/summary.html

[Dr15Jones]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_5_X IBs (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[davidlange6]

+1