incase of symlink, we should just delete it instead of calling os.chmod that...

incase of symlink, we should just delete it instead of calling os.chmod that tries to chmod the original that can raise 'Operation not permitted' error.

src/zc/buildout/rmtree.py

@@ -54,8 +54,11 @@ def rmtree (path):
     0
     """
     def retry_writeable (func, path, exc):
-        os.chmod (path, 0600)
-        func (path)
+        if func == os.path.islink:
+            os.unlink(path)
+        else:
+            os.chmod (path, 0600)
+            func (path)
 
     shutil.rmtree (path, onerror = retry_writeable)