Patch contributed by Mattijs Janssens

This method waits until all the threads have completed IO operations and
then clears any cached information about the files on disk. This
replaces the deactivation of threading by means of zeroing the buffer
size when writing and reading of a file happen in sequence. It also
allows paraFoam to update the list of available times.

Patch contributed by Mattijs Janssens
Resolves bug report https://bugs.openfoam.org/view.php?id=2962

twoPhaseMixtureThermo writes the temperatures during construction only
for them to be read again immediately after by construction of the
individual phases' thermo models. When running with collated file
handling this behaviour is not thread safe. This change deactivates
threading for the duration of this behaviour.

Patch contributed by Mattijs Janssens

Patch contributed by Mattijs Janssens

- for larger problems with a smaller region of interest, can apply a
  bounding to limit the size of the ensight geometry and fields created.

  Since the implementation uses a fvMeshSubset, there is an additional
  per-process memory overhead.

  A high output frequency should be avoided with moving meshes, since
  this indirectly forces a frequent update of the submesh.

- a quick test for which side of the face a point is located

- const version of offsets().

- empty() method to test for empty offsets, or zero overall size

- reset() methods for reseting the sizes. For example, when the context
  has shifted slightly.

- localStart() methods, similar to localSize() methods

STYLE: make globalIndex single parameter constructors explicit

- added line::last() for consistency with edge::last()

- adjusted unitVec() to return Zero for small vectors.
  Consistent with VectorSpace normalised() and vector::normalise()

- The function of the nil class is now taken by zero::null.

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.

- rework to use bitSet for more flexibility

- extract a list of the HashTable values, optionally sorted.

- when both min and max are required, this is more efficient than
  traversing the list twice.