new management for sampledSurface(s)

//- Does the surface need an update?
        virtual bool needsUpdate() const = 0;

        //- Mark the surface as needing an update.
        //  May also free up unneeded data.
        //  Return false if surface was already marked as expired.
        virtual bool expire() = 0;

        //- Update the surface as required.
        //  Do nothing (and return false) if no update was required
        virtual bool update() = 0;

    The constructors for the derived classes should generally start in a
    'expired' condition (ie, needsUpdate() == true) and rely on a subsequent
    call to the update() method to complete the initialization. Delaying the
    final construction as late as possible allows the construction of
    surfaces that may depend on intermediate calculation results (eg,
    iso-surfaces) and also avoids the unnecessary reconstruction of surfaces
    between sampling intervals.

    It is the responsibility of the caller to ensure that the surface
    update() is called before the surface is used.  The update() method
    implementation should do nothing when the surface is already up-to-date.

applications/utilities/postProcessing/sampling/sample/sampleDict

@@ -109,26 +109,24 @@ sets
 //      plane : values on plane defined by point, normal.
 //      patch : values on patch.
 //
-// 1] planes are triangulated by default
-// 2] patches are not triangulated by default
+// 1] patches are not triangulated by default
+// 2] planes are always triangulated
+// 3] iso-surfaces are always triangulated
 surfaces
 (
     constantPlane
     {
-        type            plane;
+        type            plane;    // always triangulated
         basePoint       (0.0501 0.0501 0.005);
         normalVector    (0.1 0.1 1);
 
         //- Optional: restrict to a particular zone
         // zoneName        zone1;
-
-        // Optional: whether to leave as faces or triangulate (=default)
-        triangulate     false;
     }
 
     interpolatedPlane
     {
-        type            plane;
+        type            plane;    // always triangulated
         // make plane relative to the coordinateSystem (Cartesian)
         coordinateSystem
         {
@@ -136,7 +134,6 @@ surfaces
         }
         basePoint       (0 0 0);
         normalVector    (0.1 0.1 1);
-        triangulate     false;
         interpolate     true;
     }
 
@@ -145,6 +142,7 @@ surfaces
         type            patch;
         patchName       movingWall;
         // Optional: whether to leave as faces (=default) or triangulate
+        // triangulate     false;
     }
 
     movingWall_interpolated
@@ -153,26 +151,27 @@ surfaces
         patchName       movingWall;
         interpolate     true;
         // Optional: whether to leave as faces (=default) or triangulate
+        // triangulate     false;
     }
 
     interpolatedIso
     {
         // Iso surface for interpolated values only
-        type            isoSurface;
+        type            isoSurface;    // always triangulated
         isoField        rho;
         isoValue        0.5;
         interpolate     true;
-        //regularise      false;    //optional: do not simplify
+        // regularise      false;    // Optional: do not simplify
     }
     constantIso
     {
-        // Iso surface for constant values. Guarantees triangles to not
-        // cross cells.
-        type            isoSurfaceCell;
+        // Iso surface for constant values.
+        // Triangles guaranteed not to cross cells.
+        type            isoSurfaceCell;    // always triangulated
         isoField        rho;
         isoValue        0.5;
         interpolate     false;
-        //regularise      false;    //optional: do not simplify
+        // regularise      false;    // Optional: do not simplify
     }
 );