tests/test-gendoc-zh_TW.t

py3: have bytes version of os.getenv

os.getenv() on python 3 deals with unicodes. If we want to pass bytes. we have
os.getenvb() which deals with bytes. This patch adds up a pycompat.osgetenv
which deals with bytes on both python 2 and 3.

#require docutils gettext

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