Update ab to accept URLs with IPv6 literal address strings (in the

Update ab to accept URLs with IPv6 literal address strings (in the
format described in RFC 2732), and to build Host header fields in
the same format.  This allows IPv6 literal address strings to be
used with ab.  This support has been tested against Apache 1.3 with
the KAME patch, but Apache 2.0 does not yet work with this format
of the Host header field.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@87054 13f79535-47bb-0310-9956-ffa450edef68