Add test for oldcmarkup warning

tests/test_build_html.py

@@ -39,6 +39,9 @@ http://www.python.org/logo.png
 reading included file u'wrongenc.inc' seems to be wrong, try giving an \
 :encoding: option
 %(root)s/includes.txt:4: WARNING: download file not readable: nonexisting.png
+%(root)s/objects.txt:79: WARNING: using old C markup; please migrate to \
+new-style markup \(e.g. c:function instead of cfunction\), see \
+http://sphinx.pocoo.org/domains.html
 """
 
 HTML_WARNINGS = ENV_WARNINGS + """\