issue2551097 - fix call to markdown2 - fix fenced code blocks. The invocation of fenced codeblock support in markdown2 was wrong. With this fixed the code that was used to test markdown processor exception handling no longer works. Fixed test case to make it pass. Added new test with invalid markdown that tests markdown exception handling. Also renamed test to include markdown. Makes using -k option in run_tests easier.

try:
    from html import escape as html_escape_  # python 3

    def html_escape(str, quote=False):
        # html_escape under python 3 sets quote to true by default
        # make it python 2 compatible
        return html_escape_(str, quote=quote)
except ImportError:
    # python 2 fallback
    from cgi import escape as html_escape  # noqa: F401