functionObjects::grad: Avoid cache conflict with 'postProcess' utility

Resolves bug-report http://bugs.openfoam.org/view.php?id=2350

src/OpenFOAM/db/functionObjects/regionFunctionObject/regionFunctionObjectTemplates.C

@@ -59,7 +59,7 @@ bool Foam::functionObjects::regionFunctionObject::store
     if (cacheable && fieldName == tfield().name())
     {
         WarningInFunction
-            << "Cannot store cache-able field with the named used in the cache."
+            << "Cannot store cache-able field with the name used in the cache."
             << nl
             << "    Either choose a different name or cache the field"
             << "    and use the 'writeObjects' functionObject."

src/functionObjects/field/grad/gradTemplates.C

@@ -39,7 +39,7 @@ bool Foam::functionObjects::grad::calcGrad()
         (
             resultName_,
             fvc::grad(lookupObject<VolFieldType>(fieldName_)),
-            true
+            mesh_.changing() && mesh_.cache(resultName_)
         );
     }
     else if (foundObject<SurfaceFieldType>(fieldName_))
@@ -48,7 +48,7 @@ bool Foam::functionObjects::grad::calcGrad()
         (
             resultName_,
             fvc::grad(lookupObject<SurfaceFieldType>(fieldName_)),
-            true
+            mesh_.changing() && mesh_.cache(resultName_)
         );
     }
     else