C++: properly cast destination signals in map constructors.
C++: properly cast destination signals in map constructors.

radarsat1/libmapper,johnty/libmapper,libmapper/libmapper,libmapper/libmapper,johnty/libmapper,radarsat1/libmapper,malloch/libmapper,radarsat1/libmapper,malloch/libmapper,malloch/libmapper,radarsat1/libmapper,johnty/libmapper,radarsat1/libmapper,libmapper/libmapper,malloch/libmapper,johnty/libmapper,libmapper/libmapper,johnty/libmapper,malloch/libmapper,malloch/libmapper,libmapper/libmapper,libmapper/libmapper