Added checks to groupBy to prevent the selection of improper opCols and groups.
Added checks to groupBy to prevent the selection of improper opCols and groups.

jmarshall/bedtools2,arq5x/bedtools2,arq5x/bedtools2,arq5x/bedtools2,arq5x/bedtools2,arq5x/bedtools2,jmarshall/bedtools2,jmarshall/bedtools2,jmarshall/bedtools2,jmarshall/bedtools2