Faile to build on Qt4.8

[Tambellini]

- Use any Qt 4.8 SDK
- open Carve.pro with Qt Creator (I use 2.4.1 but does nt matter)
- try to build
- see :
c:\Qt\4.8.3\include\QtCore\..\..\src\corelib\global\qglobal.h:2505: error: 'dynamic_cast_will_always_fail_because_rtti_is_disabled' is not a member of 'CarveSVGElement*'
because of:
        CarveSVGElement* svg = dynamic_cast<CarveSVGElement*>(docNode);

This is due to the fact that "now" (at least Qt 4.8) Qt is no more using rtti and no more build by default with dyn cast support (QT_NO_DYNAMIC_CAST).

To build current Carve branch, it would require to rebuild the whole Qt SDK without QT_NO_DYNAMIC_CAST

It would be better to mutate carve sources from using dynamic_cast to qobject_cast.
Would need for CarveSVGElement to inherit from QObject.