update SerialMesh::stitch_meshes to throw an error if we find multiple matching nodes
update SerialMesh::stitch_meshes to throw an error if we find multiple matching nodes

Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh,Mbewu/libmesh