ENH: added functionObject::execute(int) method

- this is a provision for defining execute actions that can be called
  largely independently of the normal time-loop constraints. This can
  be useful to provide hooks for sub-cycling, or to define an action
  that can be triggered manually or on some other event.

src/OpenFOAM/db/functionObjects/functionObject/functionObject.C

@@ -141,6 +141,12 @@ bool Foam::functionObject::read(const dictionary& dict)
 }
 
 
+bool Foam::functionObject::execute(const label)
+{
+    return true;
+}
+
+
 bool Foam::functionObject::end()
 {
     return true;

src/OpenFOAM/db/functionObjects/functionObject/functionObject.H

@@ -222,13 +222,19 @@ public:
         const word& name() const;
 
         //- Read and set the function object if its data have changed
-        virtual bool read(const dictionary&);
+        virtual bool read(const dictionary& dict);
 
         //- Called at each ++ or += of the time-loop.
         //  postProcess overrides the usual executeControl behaviour and
         //  forces execution (used in post-processing mode)
         virtual bool execute() = 0;
 
+        //- Execute using the specified subIndex.
+        //  The base implementation is a no-op.
+        //  \param subIndex an execution sub-index corresponding to a
+        //      sub-cycle or something similar.
+        virtual bool execute(const label subIndex);
+
         //- Called at each ++ or += of the time-loop.
         //  postProcess overrides the usual writeControl behaviour and
         //  forces writing always (used in post-processing mode)
@@ -245,9 +251,11 @@ public:
         virtual bool filesModified() const;
 
         //- Update for changes of mesh
+        //  The base implementation is a no-op.
         virtual void updateMesh(const mapPolyMesh& mpm);
 
         //- Update for changes of mesh
+        //  The base implementation is a no-op.
         virtual void movePoints(const polyMesh& mesh);
 };