- missing indexing caused the real radius to be largely ignored
  when useRealRadius = true

- the original intention was to avoid vtp output when the clouds are
  empty anyhow. However, it is useful for post-processing to have
  clouds with zero parcels (eg, before the start of injection).

  Pruning of empty clouds is now an option in the vtkCloud dictionary
  controls, with the default being false (no pruning). This represents
  a non-breaking change in behaviour since it generates more output
  than previously.

  Example,
  {
      type    vtkCloud;
      //- Suppress writing of empty clouds (default: false)
      prune   true;
  }

- use "min:xxx" format for AMIInterpolation as well

Merge branch 'develop-pre-release' of develop.openfoam.com:Development/OpenFOAM-plus into develop-pre-release

- the backend script should not be accessible from the PATH.
  Using deprecated/ adds a level of documentation.

- functionObjectLibs -> libs
- redirectType -> name
- change deprecated writeCompression flags types to Switch.

- cleanup some trailing ';;' from some dictionaries

STYLE: separate areaNormal/unitNormal method for primitives (issue #885)

See merge request OpenFOAM-plus!208

- regularise referencing of OpenFOAM env variables, sources etc.

- The problem is not 100% reproducible, but be somewhat conservative
  and now only close(stdin) for pure background (daemon-like) use of
  Foam::system(), where it can be useful.

  Using Foam::system() for launching background processes is currently
  only used for the doc browser.

- since 1612, FOAM_INST_DIR and foamInstDir longer have any
  special meanings when sourcing the bashrc or cshrc files.
  Thus no need for special treatment in any of the dispatch wrappers.

  Retained FOAM_INST_DIR as (unexported) variable in etc/bashrc,
  just in case people are using patched versions of etc/bashrc
  as part of their installation.

ENH: relax prefix restrictions on foamCreateVideo (issue #904)

- shift the implicit '.' to be part of the default prefix. This allows
  things like "-image myimages_00" to work as might be expected.

Feature processor level of detail (LOD)

See merge request OpenFOAM-plus!210