rebase 1604: fixes to HLTrigger.HLTcore.TriggerExpressionData and adapta...

Rebase 1604: fixes to HLTrigger.HLTcore.TriggerExpressionData and adaptations to the multithreaded fwk
This pull request replaces #1604 (which will be then removed) so that only the three really modified files enter in the PR, while getting rid of the 314 additional ones automatically added when rebasing the original PR