tests/test-locale.t

chgserver: discard buffered output before restoring fds (issue6207)

On Python 3, flush() appears not discarding buffered data on EPIPE, and
the buffered data will be carried over to the restored stdout.

  $ LANG=nonexistent LC_ALL=nonexistent LANGUAGE=nonexistent hg version -q
  Mercurial Distributed SCM (version *) (glob)