py3: replace os.pathsep with pycompat.ospathsep
os.pathsep returns unicode on Python 3. We already have pycompat.ospathsep
which return bytes on Python 3. This patch replaces all the occurrences of
os.pathsep in the codebase (excluding tests) to pycompat.ospathsep.
#require docutils gettext
$ $TESTDIR/check-gendoc ru
checking for parse errors