Moved the declaration of wxEVT_NULL to event.cpp and made it extern in the header to solve BCC compilation issues

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@9823 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/event.cpp

@@ -111,6 +111,7 @@ wxList *wxPendingEvents = (wxList *)NULL;
 // common event types are defined here, other event types are defined by the
 // components which use them
 
+DEFINE_EVENT_TYPE(wxEVT_NULL)
 DEFINE_EVENT_TYPE(wxEVT_COMMAND_BUTTON_CLICKED)
 DEFINE_EVENT_TYPE(wxEVT_COMMAND_CHECKBOX_CLICKED)
 DEFINE_EVENT_TYPE(wxEVT_COMMAND_CHOICE_SELECTED)