Backported menu fix from 2.5

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_4_BRANCH@29753 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/menucmn.cpp

@@ -406,6 +406,7 @@ wxMenuItem *wxMenuBase::DoRemove(wxMenuItem *item)
     if ( submenu )
     {
         submenu->SetParent((wxMenu *)NULL);
+        if (submenu->IsAttached()) submenu->Detach();
     }
 
     return item;