Attempt to fix gcc 4.9.0 issue.
Merge pull request #2364 from ktf/fix-gcc4.9.0-TrackPropagation-SteppingHelixPropagator

Reco -- Attempt to fix gcc 4.9.0 issue.
Merge remote branch 'origin/CMSSW_7_1_X' into CMSSW_7_0_X