py3: convert system strings to bytes in doctest of formatter.py

py3: rewrite stdout hack of doctest by using ui.pushbuffer() We can't use pycompat.stdout here because the doctest runner replaces sys.stdout with a string buffer.

py3: use bytes os.sep in doctest of pathutil.py

py3: fix doctests in patch.py to be compatible with Python 3 We were lucky that parsepatch() could concatenate a character slice as if it were a list of chunks.