Use toSomeType() instead of operator SomeType in ScriptValue.

This means that we are more explicit about type conversions.
Also use override specifiers for overriden virtual functions in ScriptValue.

src/gui/control/card_list.cpp

@@ -319,7 +319,7 @@ int CardListBase::OnGetItemImage(long pos) const {
 wxListItemAttr* CardListBase::OnGetItemAttr(long pos) const {
   if (!set->game->card_list_color_script) return nullptr;
   Context& ctx = set->getContext(getCard(pos));
-  item_attr.SetTextColour(*set->game->card_list_color_script.invoke(ctx));
+  item_attr.SetTextColour(set->game->card_list_color_script.invoke(ctx)->toColor());
   return &item_attr;
 }
 

src/gui/set/console_panel.cpp

@@ -508,7 +508,7 @@ void ConsolePanel::exec(String const& command) {
       message->bitmap = wxBitmap(image);
     } else if (type == SCRIPT_COLOR) {
       message->text = result->toCode();
-      Color color = result->operator Color();
+      Color color = result->toColor();
       wxImage image(30,20);
       fill_image(image,color);
       set_alpha(image, color.Alpha() / 255.0);

src/gui/value/choice.cpp

@@ -253,7 +253,7 @@ size_t DropDownChoiceList::selection() const {
       return 0;
     } else {
       // run default script to find out what the default choice would be
-      String default_choice = *field().default_script.invoke( cve.viewer.getContext() );
+      String default_choice = field().default_script.invoke( cve.viewer.getContext() )->toString();
       default_id = group->choiceId(default_choice);
     }
   }

src/gui/value/color.cpp

@@ -107,7 +107,7 @@ size_t DropDownColorList::selection() const {
     return 0;
   } else if (hasDefault()) {
     // evaluate script to find default color
-    default_color = *field().default_script.invoke(cve.viewer.getContext());
+    default_color = field().default_script.invoke(cve.viewer.getContext())->toColor();
   }
   return selection;
 }