Add m4 to externals being built.
Merge branch 'IB/CMSSW_6_2_X/stable' of github.com:cms-sw/cmsdist into IB/CMSSW_6_2_X/stable
Merge pull request #77 from ktf/IB/CMSSW_6_2_X/stable

Ib/cmssw 6 2 x/stable