Added a comment explaining what vars_to_save is for in parse.cpp (DAGMan).
Added a comment explaining what vars_to_save is for in parse.cpp
(DAGMan).

neurodebian/htcondor,htcondor/htcondor,htcondor/htcondor,neurodebian/htcondor,htcondor/htcondor,neurodebian/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,neurodebian/htcondor,neurodebian/htcondor,neurodebian/htcondor,neurodebian/htcondor,neurodebian/htcondor,neurodebian/htcondor,htcondor/htcondor