ENH: read support for EnSight single-file transient (#3154)

- the ensightReadFile init() now automatically sets up binary/ascii
  (for geometry files) and checks for the transient "BEGIN TIME STEP"
  marker. If found, will also populate the file offsets for each of
  the timesteps.  If no corresponding footer is found (which would be
  very inefficient), it simply pretends that there is only a single
  time step instead of performing a costly file scan.

- parsing of the ensight case file now also supports the use of

      filename numbers:

  as an alternative to

      filename start number:
      filename increment:

- improved parsing robustness of "time values:" entry.
  Can now also have contents on the same line as the introducer.

ENH: base-level adjustments for writing transient single-file

- beginGeometry() is now separated out from file creation.

- in append mode, ensightFile and ensightGeoFile will attempt to
  parse existing time-step information.

src/functionObjects/utilities/ensightWrite/ensightWrite.C

@@ -237,7 +237,7 @@ bool Foam::functionObjects::ensightWrite::write()
         // Treat all geometry as moving, since we do not know a priori
         // if the simulation has mesh motion later on.
         autoPtr<ensightGeoFile> os = ensCase_().newGeometry(true);
-        ensMesh_().write(os);
+        ensMesh_().write(os.ref());
     }