std::hash<Point> overload
std::hash<Point> overload

unordered_set<Point> and unordered_map<Point,foo> can be useful, at
least in cases like our triangulators where we know a priori we don't
have overlapping points.

libMesh/libmesh,dschwen/libmesh,jwpeterson/libmesh,jwpeterson/libmesh,jwpeterson/libmesh,dschwen/libmesh,libMesh/libmesh,libMesh/libmesh,dschwen/libmesh,dschwen/libmesh,jwpeterson/libmesh,dschwen/libmesh,jwpeterson/libmesh,dschwen/libmesh,libMesh/libmesh,libMesh/libmesh,dschwen/libmesh,libMesh/libmesh,jwpeterson/libmesh,jwpeterson/libmesh,dschwen/libmesh,libMesh/libmesh,libMesh/libmesh,jwpeterson/libmesh