doc/translator.py unified for Python 2.6+ and Python 3.0+

- Open() replaced by xopen() that internally uses the encoding argument
  only for Python 3. The earlier usage of the codecs module and of the
  prefixed unicode string literals was removed.
- Some lists of prototypes were sorted to get the same translator report
  for different versions of Python.
- The local dedent() definition was replaced by textwrap.dedent().
  (The older versions of Python did not have the module.)
- Tested on Windows for Python 2.6.0, 2.7.7, 3.0.1, and 3.4.1.