[Qt-interest] qobject_cast<>() and objects from dynamically loadedlibraries

[Acenes]

Make sure to use the Qt export/import declarations so the static metaobject 
is also exported from the dll:

#ifdef BUILDING_MY_DLL
# define MYDLL_EXPORT Q_DECL_EXPORT
#else
# define MYDLL_EXPORT Q_DECL_IMPORT
#endif

class MYDLL_EXPORT Base: public QWidget
{
 Q_OBJECT
};

class MYDLL_EXPORT SomeImpl: public Base
{
 Q_OBJECT
};