1) wxEVT_COMMAND_TREE_EXPANDING event now generated
2) tree control doesn't not delete children on branch collapse any more
3) migging image list and image-related functions added (but not yet
implemented)
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@160 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775