Thanks for the patch.

There seems to be a race remaining here:

+        try:
+            if os.path.islink(path):
+                # symlinks to directories are forbidden, see bug #1669
+                raise OSError("Cannot call rmtree on a symbolic link")
+        except OSError:
+            onerror(os.path.islink, path, sys.exc_info())
+            # can't continue even if onerror hook returns
+            return
+        fd = os.open(path, os.O_RDONLY)

Someone could change `path` to be a symlink between the calls to islink() and open(). You probably need to stat the fd instead.

Some other things:
- if close() is meant to be a private helper, it should be named _close()
- instead of a bare "except" in close(), use "except EnvironmentError" or "except OSError"

I haven't looked at the tests yet.