add TSG Mixing flat 20-50 mixing scenario
Merge pull request #3372 from mdhildreth/7_0_X_Add_TSG_Mixing_Scenario

add TSG Mixing flat 20-50 mixing scenario
Merge remote branch 'origin/CMSSW_7_0_X' into CMSSW_7_0_X
Rename JetIdParams_cfi.py to puJetIdParams_cfi.py.

This avoids name conflict on OSX due to case insensitive file system
there.