- stream each patch entry and modify the output directly.
  This is slightly ugly, but avoids these key issues:

    - cannot write local boundary information since it will have the
      wrong sizes and processor boundaries etc.
    - cannot 'fake' a different set of boundary patches without a
      full mesh to reference.

ENH: respect "requested.partition-offsets" when writing polyMesh as coherent

- normally the mesh partitioning corresponds to the mesh ranks.
  However, when preparing a serial mesh with proper cell ordering
  for a parallel coherent case, the writing will occur in serial.

  For this case, use the polyMesh.data() member [a dictionary]
  to pass the desired partitioning into the writing backend.

ENH: fix search for polyMesh/data.bp/ and polyMesh/coherent

- use the updated Time::findInstance() with new optional parameter to
  avoid re-testing of the result.

ENH: remove old polyMesh/data.bp directory before writing

- avoids an endless appending when the OpenFOAM utility is ostensibly
  in "-overwrite" mode, or when repeatedly calling something like
  blockMesh.