Use Emacs compatible coding system

Emacs doesn't recognize "utf8" as a valid coding system. The correct
name is "utf-8". This is in line with the UTF-8 FAQ:

  http://www.cl.cam.ac.uk/~mgk25/unicode.html#utf-8

  The official name and spelling of this encoding is UTF-8, where UTF
  stands for UCS Transformation Format. Please do not write UTF-8 in
  any documentation text in other ways (such as utf8 or UTF_8), unless
  of course you refer to a variable name and not the encoding itself.

test/templates/chs_unicode.html

-## -*- coding:utf8 -*-
+## -*- coding:utf-8 -*-
 <%
  msg = u'新中国的主席'
 %>

test/templates/chs_unicode_py3k.html

-## -*- coding:utf8 -*-
+## -*- coding:utf-8 -*-
 <%
  msg = '新中国的主席'
 %>

test/templates/chs_utf8.html

-## -*- coding:utf8 -*-
+## -*- coding:utf-8 -*-
 <%
  msg = '新中国的主席'
 %>