VSubSet(char* namein, VSpace& s, GeObList& v)
Builds a vector subset of vector space s, with debug name in buffer namein. The subset creates its own copy of the name. The geometric objects in list v, after mapping into space s if necessary, span the subset.
VSubSet(SubSet& s)
Used to downcast a general subset to a vector subset. Only succeeds if the general subset is holding a vector subset.