Misc multithreading fixes.

- FastJet fixes from Chris.
- TMVA fixes from Chris.
- Adaptations to get sherpa to compile.

This is the same set of changes valdiated by @slava77 between
CMSSW_7_2_DEVEL_X_2014-05-29-1400 and CMSSW_7_2_X_2014-05-29-1400.

Summary from Slava:

> Results in CMSSW_7_2_DEVEL_X_2014-05-29-1400    and
> CMSSW_7_2_X_2014-05-29-1400
> look the same based on fwlite-based diffs and DQM comparisons.
> tests included the short matrix and some higher stat "extended tests"
> (dijet, ele/mu/pho guns and ttbar with PU).
Merge pull request #752 from ktf/backport-mt-fixes

Backport multithreading fixes.
Merge remote branch 'origin/IB/CMSSW_7_1_X/stable' into IB/CMSSW_7_0_X/stable