- multiply-connected edges can arise at the centre of a "star"
  connection or because the patch faces are actually baffles.

- In the serial case these internal edges are also rather dubious in
  terms of modelling. However, when they are split across multiple
  processors there can only be a single processor-to-processor
  connectivity.

  We don't necessary have enough information to know how things should
  be connected, so connect pair-wise as the first remedial solution

- Any extra dangle edges are relegated to an 'ignore' faPatch
  to tag as needing different handling.