Update to GeneratorInterface/SherpaInterface

[thuer]

Updated the Interface to use newer function calls of Sherpa in order to get HepMC output
some of the changes are needed in order to use Sherpa 2.1.1

[cmsbuild]

A new Pull Request was created by @thuer for CMSSW_6_2_X.

Update to GeneratorInterface/SherpaInterface

It involves the following packages:

GeneratorInterface/SherpaInterface

@vciulli, @nclopezo, @thuer, @cmsbuild, @bendavid, @Degano can you please review it and eventually sign? Thanks.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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@Degano you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[bendavid]

Please make sure the corresponding changes go into pull requests for 72x and 71x as well. (And the 72x version will have to be merged in first)

[cmsbuild]

+1
Tested at: a1fe779
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-4273/79/summary.html

[bendavid]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_6_2_X IBs unless changes or unless it breaks tests. @Degano can you please take care of it?

[cmsbuild]

+1
Tested at: 3637356
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-4273/80/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_6_2_X IBs unless changes (tests are also fine). @Degano can you please take care of it?