Avoid returning EDGE position for 2 nodes on the same EDGE, while the
medium node should be on FACE. The case is a triangle whose 3 nodes are on
the same EDGE. The worst is that in this case the medium node which
is logically on FACE falls to a straight EDGE, as the triangle is of
zero area (thanks to MEFISTO)
std::pair<int, TopAbs_ShapeEnum> GetMediumPos(const SMDS_MeshNode* n1,
const SMDS_MeshNode* n2,
+ const bool useCurSubShape=false);