Forward port recent changes on the 2.8 branch to HEAD

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@46083 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

wxPython/demo/TreeMixin.py

@@ -1,6 +1,10 @@
 import wx, wx.lib.customtreectrl, wx.gizmos
-import treemixin
+try:
+    import treemixin 
+except ImportError:
+    from wx.lib.mixins import treemixin
 
+overview = treemixin.__doc__
 
 class TreeModel(object):
     ''' TreeModel holds the domain objects that are shown in the different