functionObjectList::readFunctionObject: Added support for region specification

Now the postProcess utility '-region' option works correctly, e.g. for
the chtMultiRegionSimpleFoam/heatExchanger case

postProcess -region air -func "mag(U)"

calculates 'mag(U)' for all the time steps in region 'air'.

src/OpenFOAM/db/functionObjects/functionObjectList/functionObjectList.H

@@ -218,7 +218,8 @@ public:
         (
             const string& funcNameArgs0,
             dictionary& functionsDict,
-            HashSet<word>& requiredFields
+            HashSet<word>& requiredFields,
+            const word& region = word::null
         );
 
         //- Read and set the function objects if their data have changed