py3: use bytes stdout in test-check-help.t

Setting stdout to binary seemed to have no effect on Windows, as it was
appending a literal '\r' to each topic keyword.  This also stops prepending 'b'
to the topic on all platforms as well.

tests/test-check-help.t

@@ -1,30 +1,31 b''
 #require test-repo
 
   $ . "$TESTDIR/helpers-testrepo.sh"
 
   $ cat <<'EOF' > scanhelptopics.py
   > from __future__ import absolute_import, print_function
   > import re
   > import sys
   > if sys.platform == "win32":
   >     import msvcrt
   >     import os
   >     msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
+  > stdout = getattr(sys.stdout, 'buffer', sys.stdout)
   > topics = set()
   > topicre = re.compile(br':hg:`help ([a-z0-9\-.]+)`')
   > for fname in sys.argv:
   >     with open(fname, 'rb') as f:
   >         topics.update(m.group(1) for m in topicre.finditer(f.read()))
   > for s in sorted(topics):
-  >     print(s)
+  >     stdout.write(b'%s\n' % s)
   > EOF
 
   $ cd "$TESTDIR"/..
 
 Check if ":hg:`help TOPIC`" is valid:
 (use "xargs -n1 -t" to see which help commands are executed)
 
   $ testrepohg files 'glob:{hgdemandimport,hgext,mercurial}/**/*.py' \
   > | sed 's|\\|/|g' \
   > | xargs "$PYTHON" "$TESTTMP/scanhelptopics.py" \
   > | xargs -n1 hg help --config extensions.phabricator= > /dev/null