add TSG Mixing flat 20-50 mixing scenario (50 ns)
Add flat PU 20-50, 50ns
Merge pull request #4981 from franzoni/fw-port-TSG-pu-scenario-CMSSW_7_1_X_2014-08-18-1400

Fw port tsg pu scenario cmssw 7 1 x 2014 08 18 1400