Add DMTCP to AthDerivationExternals, 1.0 branch (2017.06.20.)
Added DMTCP to the externals built by AthDerivationExternals.
This is needed because 21.0 started using this external, and I want to merge all changes from 21.0 into 21.2.
Added DMTCP to the externals built by AthDerivationExternals.
This is needed because 21.0 started using this external, and I want to merge all changes from 21.0 into 21.2.