v5.0: First SL6 release

Please use v5.0.1 instead, which fixes a bug that could cause crashes in some circumstances (#166)

This is the first SLC6 release for HiggsAnalysis/CombinedLimit, that can be used on CMSSW_7_1_5 (or later 7.1.X) on the slc6_amd64_gcc481 architecture.

It includes everything in the v4.0-sl5 release plus some pdfs needed for combination with ATLAS.