added mapper_router_add_blank_mapping function
added mapper_router_add_blank_mapping function

libmapper/libmapper,radarsat1/libmapper,malloch/libmapper,libmapper/libmapper,libmapper/libmapper,johnty/libmapper,davidhernon/libmapper,davidhernon/libmapper,johnty/libmapper,davidhernon/libmapper-admin2,johnty/libmapper,malloch/libmapper,libmapper/libmapper,davidhernon/libmapper,malloch/libmapper,libmapper/libmapper,johnty/libmapper,malloch/libmapper,davidhernon/libmapper,davidhernon/libmapper-admin2,radarsat1/libmapper,libmapper/libmapper,radarsat1/libmapper,davidhernon/libmapper-admin2,radarsat1/libmapper,davidhernon/libmapper,malloch/libmapper,malloch/libmapper,davidhernon/libmapper-admin2,radarsat1/libmapper,johnty/libmapper,davidhernon/libmapper-admin2