changes to setup_git.sh file. Works for pre12 and pre13

Hi Shervin, when I edit the file like this and run ./git_setup.sh CMSSW_7_0_0_pre13, then run alcaSkimming.py on testFile.root, everything works!

Let me know if there is a better solution for my change on lines 65 and 66.

All the best,

Louie