Added -g option and descriptor to intersect help message.
Added -g option and descriptor to intersect help message.

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