added return_outlet_id to set_watershed_BC
added return_outlet_id to set_watershed_BC

cmshobe/landlab,amandersillinois/landlab,laijingtao/landlab,laijingtao/landlab,RondaStrauch/landlab,cmshobe/landlab,Carralex/landlab,landlab/landlab,RondaStrauch/landlab,landlab/landlab,ManuSchmi88/landlab,Carralex/landlab,ManuSchmi88/landlab,cmshobe/landlab,csherwood-usgs/landlab,ManuSchmi88/landlab,Carralex/landlab,amandersillinois/landlab,landlab/landlab,csherwood-usgs/landlab,RondaStrauch/landlab