cmssw: fetch sources from GitHub

Signed-off-by: David Abdurachmanov <davidlt@cern.ch>
Merge remote-tracking branch 'origin/IB/CMSSW_6_2_X/stable' into IB/CMSSW_6_2_X/devel-gcc472
Merge remote-tracking branch 'origin/IB/CMSSW_6_2_X/devel-gcc472' into IB/CMSSW_6_2_X/slc6_amd64_gcc480