Correctly parse an IPv6 literal host specification in an absolute URL

in the request line.

- Fix handling of brackets [ ] surrounding the IPv6 address.
- Skip parsing r->hostname again if not necessary.
- Do some checks that the IPv6 address is sane. This is not done by
  apr_parse_addr_port().


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1426827 13f79535-47bb-0310-9956-ffa450edef68