BUG: ensightSurfaceReader - enabled reading of data from sub-directory and updated field mask (See #215)

ENH: distinguish OpenFOAM version for user-coding (fixes #195)

The pre-processor macro 'OPENFOAM_PLUS' is defined with a numerical
value equal to the currently compatible version number.

This can be used judiciously within user coding to help with minor
differences between OpenFOAM versions. For example,

    #ifdef OPENFOAM_PLUS
        #if (OPENFOAM_PLUS >= 1612)
        ...
        #endif
    #endif

or simply

    #if (OPENFOAM_PLUS >= 1612)
    ...
    #endif

See merge request !56

replace system() call with vfork/exec combination (issue #185)

Tested systemCall function object, dynamicCode, but should be rechecked with IB+openmpi
@Prashant

See merge request !55

ENH: OSspecific - softlink handling (fixes #164)

Links are followed in most cases, with some notable exceptions:

- mv, mvBak:
  renames the link, not the underlying file/directory

- rmDir:
  remove the symlink to a directory, does not recurse into the
  underlying directory

See merge request !51

The pre-processor macro 'OPENFOAM_PLUS' is defined with a numerical
value equal to the currently compatible version number.

This can be used judiciously within user coding to help with minor
differences between OpenFOAM versions. For example,

    #ifdef OPENFOAM_PLUS
        #if (OPENFOAM_PLUS >= 1612)
        ...
        #endif
    #endif

or simply

    #if (OPENFOAM_PLUS >= 1612)
    ...
    #endif

Fixes #192

so will be out of date (w.r.t bounding box, subdivisions) when the mesh moves.
Only when all cells stays in all the same boxes can you skip rebuilding it
so this was not deemed worthwhile. Fixes #172

STYLE/ENH: reduce code duplication for coded boundary conditions (issue #184)

- relocate common dictionary output into codedBase class

@Mattijs please test with a few examples as well

See merge request !54

The normal library system() command uses 'fork', which causes
problems on IB+OPENMPI.

STYLE: add Foam:: qualifier to system calls to make them easier to spot.