Bugfix for edm::FwdRef

[arizzi]

@gpetruc @rappoccio
Fix FwdRef so that at get() time it checks Availability rather than Nullness.
Should fix the access when the original collection is kept and the forward pointed is dropped.
This way should also be complaint with the implementation of edm::FwdRef::isAvailable that return true if any of the two collections is available. With old implementation despite isAvailable being true, dereferencing would throw if the fwd pointed was dropped.

See:
https://hypernews.cern.ch/HyperNews/CMS/get/edmFramework/3282.html

Similar to PR #3850

[cmsbuild]

A new Pull Request was created by @arizzi for CMSSW_7_0_X.

FwdRef and FwdPtr: Nullness and Availability are two different things

It involves the following packages:

DataFormats/Common

@cmsbuild, @Degano, @Dr15Jones, @ktf, @nclopezo can you please review it and eventually sign? Thanks.
@wmtan this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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@nclopezo, @ktf you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[cmsbuild]

+1
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-3851/156/summary.html

[Dr15Jones]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_0_X IBs unless changes (tests are also fine). @nclopezo, @ktf can you please take care of it?

[ktf]

Approved at today ORP. Merging.