Decode patch from UTF-8 while parsing from stdin

Patchwork (rightfully) hashes patches using UTF-8:

  parser.py:
    def hash_patch(str):
      […]
      hash.update(line.encode('utf-8') + '\n')

This patch makes sure that it treats the incoming data as UTF-8 as well.

Signed-off-by: martin f. krafft <madduck@madduck.net>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>