Using os.path.join for web URLs is bad
treebeard_css and treebeard_js uses os.path.join to build the URL for the css file. This fails on windows systems, as the directory seperator on windows is \ (backslash). All browsers - os independently - expect / (forward-slash).
While the files are actually found in my setup, CSS files cannot reference the images, as the path actually ends up beeing something like "http://page/static/treebeard%5Ctreebeard-admin.css"