- The test condition

      [ -n "$cur" -a ... ]

  fails if $cur starts with '-le', which bash interprets as a further
  test op. Splitting the test condition solves the problem:

      [ -n "$cur" ] && [ ... ]

- Since the local edges are oriented according to the gradient,
  they can also be used to determine the correct face orientation.

This generalizes the algorithm for future reuse.

- simple check for unique and non-negative point labels

- replaces previous pointer conversion

- uses int, without enclosing brackets.

This is not the ultimate fix; it just avoids the loops in cases where
mesh 0 is the background.

mapping.  Fixes #983

Note: this removes the option to reconstruct by setting nDomains to 1.
      You now have to explicitly use -reconstruct to reconstruct.

- more consistent with dictionary method naming. The get<> or
  getList<> returns a value, doesn't read into a existing location.

STYLE: use initial hash size 128 instead of 100 in a few places

- there were previously no hashing mechanisms for lists so they
  would fall back to the definition for primitives and hash the
  memory location of the allocated List object.

- provide a UList::Hash<> sub-class for inheritance, and also a global
  specialization for UList<T>, List<T> such that the hash value for
  List<List<T>> cascades properly.

- provide similar function in triFace to ensure that it remains
  similar in behaviour to face.

- added SymmHash to Pair, for use when order is unimportant.

STYLE: use string::hash() more consistently

- no particular reason to use Hash<word>() which forwards to
  string::hash() anyhow

- allows single or multiple entries

- With argList::noFunctionObjects() we use the logic added in
  4b933332 (issue #352)

  By removing the '-noFunctionObjects' option, we automatically
  suppress the creation of function-objects via Time (with argList
  as a parameter).
  There is generally no need in these cases for an additional

      runTime.functionObjects().off()  statement

  Use the argList::noFunctionObjects() for more direct configuration
  and reduce unnecessary clutter in the -help information.

  In previous versions, the -noFunctionObjects would have been redundant
  anyhow, so we can also just ignore it now instead.

- allows use with any container with begin(), end() and where the
  "*iterator" dereference returns a label, which is used for indexing
  into the list of points.
  This container could be labelUList, bitSet, labelHashSet, etc

- takes a direct approach of determining which cells are cut and walks
  the cell faces directly to build the resulting surface.

- better handling of corner cases.
  * Avoids redundant points when the cut passes exactly through a
    mesh point.
  * Supresses generation of duplicates faces when the plane cut
    coincides exactly with a mesh face.

- for severely concave cells where the plane cuts a face multiple times
  there is currently no remedial action taken, except to note the
  failure and unwind the insertion of the corresponding points and
  faces.