This is intended as a possibly temporary measure for processing
explicitly assigned NNCs (keywords NNC/EDITNNC/EDITNNCR) along with
those NNCs arising from numerical aquifers, and for which there is
no associate face direction.
Add a set of unit tests to probe the implementation of all MULTREGT
connection behaviours as exhibited by MULTREGTScanner member
functions getRegionMultiplier() and getRegionMultiplierNNC().