Fix momentumTensor calculation

Norm of momentumTensor should be initialized with zero
Same changes as for CMSSW_7_2_X_sherpa_2.1.1 applied to CMSSW_7_1_X
Missed to remove obsolete header
Remove tarballs from repository
Mixed up changes from 72X with 71X, reversed changes to Buildfile and FetcherRRR
Merge pull request #4292 from thuer/CMSSW_7_1_X_sherpa_2.1.1

Some changes to the SherpaInterface in line with th changes to 62X and 72X
Merge pull request #4025 from sroecker/patch-1

Fix momentumTensor calculation
Merge remote branch 'origin/CMSSW_7_1_X' into CMSSW_7_0_X