Patch from Andrea that fixes the following problems/issues:

Patch from Andrea that fixes the following problems/issues:

a) ZeroDivisionError when using the Vista selection style and calling
SelectItem; for some strange reason, sometimes the item rect is not
initialized and that generates the ZeroDivisionError when painting the
selection rectangle;
b) Added a DeleteWindow method to GenericTreeItem class, for items
that hold a widget next to them;
c) Renamed CustomTreeCtrl method IsEnabled to IsItemEnabled, otherwise
it conflicts with wx.Window.IsEnabled;
d) Now CustomTreeCtrl behaves correctly when the widget attached to an
item is narrower (in height) than the item text;

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45520 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775