Preprocess the given data, ready for parsing.

def Preprocess(self, data):
    """Preprocess the given data, ready for parsing."""
    # Add whitespace to line continuations.
    data = data.replace(":\\", ": \\")

    # Strip comments manually because sudoers has multiple meanings for '#'.
    data = SudoersFieldParser.COMMENTS_RE.sub("", data)
    return data