Fixed two CEGUI warning types.

(Std) WidgetLookManager::addWidgetLook -
Widget look and feel 'OD/ComboDropList' already exists. Replacing previous definition.

(Error) CEGUI::UnknownObjectException in function 'CEGUI::Image& CEGUI::ImageManager::get(const CEGUI::String&) const'
Image not defined:

I left those two:
(Error) Falagard::xmlHandler::elementStart - The unknown XML element 'DimOperator' was encountered while processing the look and feel file.

(Warn)	Property 'HorzExtent' is not writable so it's implicitly banned from XML. No need to ban it manually

Because those were correct in previous CEGUI versions and I'd rather make sure
how to fix those properly and they shouldn't break the game anyway.