Add [ ] brackets to list of special characters in mb_parse_url

The brackets are reserved characters and are used in URLs based on raw ipv6 addresses, [see rfc2732](http://www.ietf.org/rfc/rfc2732.txt). When the brackets are escaped, PHP's parse_url will not reliably handle such URLs. 

Prior to the introduction of mb_parse_url, \Pdp\Parser::parseUrl() would return the bracketed address as the host. Since the change, ipv6 URLs usually result in an exception, sometimes in garbage, and very rarely a correct result. This change restores the more useful behavior.