Use wxObjectDataPtr in wxSharedClientDataContainer

This is slightly more economical, both at run-time and, maybe more
importantly, at compile-time than using wxSharedPtr that we don't really
need here, simple intrusive ref counting smart pointer is enough.

src/common/clntdata.cpp

@@ -96,7 +96,7 @@ wxClientDataContainer *wxSharedClientDataContainer::GetValidClientData()
 {
     if ( !HasClientDataContainer() )
     {
-        m_data = new wxClientDataContainer;
+        m_data = new wxRefCountedClientDataContainer;
     }
     return m_data.get();
 }