Print text details in case of assertation failed errors.

    .. sourcecode:: python

        with on_error_print_details(actual_text, expected_text):
            ... # Do something

def on_error_print_details(actual, expected):
    """
    Print text details in case of assertation failed errors.

    .. sourcecode:: python

        with on_error_print_details(actual_text, expected_text):
            ... # Do something
    """
    try:
        yield
    except Exception:
        diff = difflib.ndiff(expected.splitlines(), actual.splitlines())
        diff_text = u"\n".join(diff)
        print(u"DIFF (+ ACTUAL, - EXPECTED):\n{0}\n".format(diff_text))
        if DEBUG:
            print(u"expected:\n{0}\n".format(expected))
            print(u"actual:\n{0}".format(actual))
        raise