Extract the neighbouring vertices of a mesh vertex.

Input parameters:

1. Ms → Mesh for neighbour extraction.
2. Vi → Index of mesh vertex.
3. Jc → If true, topological rather than geometrical connectivity is resolved.

Output parameters:

1. N1 → Indices of all vertices directly connected by an edge to the specified index.
2. N2 → Indices of all vertices indirectly connected to the specified vertex, i.e. antipodal vertices on quads.