ENH: avoid memory leaks for HashPtrTable, PtrMap insertion (issue #749)

- disallow insert() of raw pointers, since a failed insertion
  (ie, entry already existed) results in an unmanaged pointer.

  Either insert using an autoPtr, or set() with raw pointers or autoPtr.

- IOobjectList::add() now takes an autoPtr instead of an object reference

- IOobjectList::remove() now returns an autoPtr instead of a raw pointer

src/functionObjects/graphics/runTimePostProcessing/scene.C

@@ -122,11 +122,10 @@ void Foam::functionObjects::runTimePostPro::scene::readColours
     const dictionary& dict
 )
 {
-    const wordList colours = dict.toc();
-    forAll(colours, i)
+    const wordList colours(dict.toc());
+    for (const word& c : colours)
     {
-        const word& c = colours[i];
-        colours_.insert(c, Function1<vector>::New(c, dict).ptr());
+        colours_.insert(c, Function1<vector>::New(c, dict));
     }
 }