Trac Ticket #275 - Invalid read reported by valgrind
    
    https://fedorahosted.org/389/ticket/275
    
    Fix description: Since the matching rule type could be normalized
    and the original string could be freed in filter_normalize_ext,
    the type needs to have a duplicated string (bitwise.c, plugin_mr.c).
    
    Filter_ava functions and filter_sub functions in the syntax plugins
    need to check if the passed pblock is NULL or not before accessing
    it.