git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52919 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
2. added tests for InsertChild() 3. simplified InsertChild() code without changing what it does git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52913 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775