regIOobject, Hasher, IOobject tweak

- regIOobject: don't re-register an unregister object on rename/assignment
- Hasher: split-off HasherInt with uint32_t specializations
- IOobject: writeBanner/writeDivider return Stream for easier chaining.

... also dropped some namespace bracketing while I was at it.

src/OpenFOAM/db/IOobject/IOobject.C

@@ -30,10 +30,7 @@ License
 
 // * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
 
-namespace Foam
-{
-    defineTypeNameAndDebug(IOobject, 0);
-}
+defineTypeNameAndDebug(Foam::IOobject, 0);
 
 // * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * * //