tests/test-gendoc-zh_TW.t

py3: convert the mode argument of os.fdopen to unicodes (1 of 2)

os.fdopen() does not accepts bytes as its second argument which represent the
mode in which the file is to be opened. This patch makes sure unicodes are
passed in py3 by using pycompat.sysstr().

#require docutils gettext

  $ $TESTDIR/check-gendoc zh_TW
  checking for parse errors