- whichPatchFace() returns the (patchi, patchFacei) tuple,
  whichPatch() simply wraps whichPatchFace()

- groupNames() : similar to zones

ENH: simplify calls to faPatch/fvPatch patchField, lookupPatchField

- make second (ununsed) template parameter optional.
  Was previously needed for old compilers (2008 and earlier).