Pass seed from ProductionMechanism to BreitWignerGenerator

[s6pepaul]

No description provided.

[gluex]

Test status for this pull request: SUCCESS

Summary: /work/halld/pull_request_test/halld_sim^BreitWignerGenerator_rnd_fix_PH/tests/summary.txt
Logs: /work/halld/pull_request_test/halld_sim^BreitWignerGenerator_rnd_fix_PH/tests/log

Build log: /work/halld/pull_request_test/halld_sim^BreitWignerGenerator_rnd_fix_PH/make_BreitWignerGenerator_rnd_fix_PH.log
Build report: /work/halld/pull_request_test/halld_sim^BreitWignerGenerator_rnd_fix_PH/report_BreitWignerGenerator_rnd_fix_PH.txt
Location of build: /work/halld/pull_request_test/halld_sim^BreitWignerGenerator_rnd_fix_PH

[mashephe]

This is a good change to support reproducibility. Just a note that this ProductionMechanism class will become obsolete with the new FixedTargetGenerator. If anyone is writing a new generator, it would make sense to write it around FixedTargetGenerator.

[mashephe]

This PR has been closed, but for an upcoming PR I'm going to make a small change to this implementation. I think it would be generally better if the classes held their own instance of the TRandom class each with settable seed. As implemented above, setting the seed affects the global gRandom instance. While this should have the desired effect of reproducible results with the same seed it introduces a potential complexity in how the sequence of random numbers might depend on other classes using the same global random number generator.