Fix exception to action table lifetime

[wmtan]

This is a purely technical fix for a segmentation fault observed by Mike Hildreth when running workflows using data premixing.
An ExceptionToActionTable object is used to determine the course of action after an exception is caught.
Unfortunately, in the class that handles processing premixed data, an ExceptionToActionTable was constructed as a temporary on the stack whose lifetime was over before it was used.
This fix allocates it on the heap, held by a std::unique_ptr, making it's lifetime the same as the containing class.
This problem does not exist prior to 7_0_X as the affected code was new for 7_0_X.

[cmsbuild]

A new Pull Request was created by @wmtan for CMSSW_7_1_X.

Fix exception to action table lifetime

It involves the following packages:

Mixing/Base

@cmsbuild, @civanch, @Degano, @mdhildreth, @nclopezo can you please review it and eventually sign? Thanks.
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@nclopezo, @ktf you are the release manager for this.
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[civanch]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes or unless it breaks tests. @nclopezo, @ktf can you please take care of it?

[cmsbuild]

+1
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-2595/274/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes (tests are also fine). @nclopezo, @ktf can you please take care of it?