subvertpy_wrapper: fix files and directories batons handling The subvertpy wrapper was not recording and passing back the batons returned by calls such as open_file() or open_directory(). Instead, it was relying on knowledge about the HgEditor class and was passing the path argument. Its behaviour was therefore not exactly the same as the swig one because HgEditor sometimes tests the input baton and skips None ones, usually generated for ignored entries. Also, AbstractEditor was translating open_root() into open_directory(''), while the former, not implemented by HgEditor, was supplied as a default implementation by the swig bindings. The behaviour was different again. This patch was not motivated by any known bug but batons are interesting as they help control edited entries lifetime. We may use them to reduce replay mode memory consumption.