merge this fix from 2.1-dev:

Fix ap_construct_url() so that it surrounds IPv6 literal address
strings with [].  This fixes certain types of redirection.

PR:           19207
Reviewed by:  Bill Stoddard, Thom May


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@99786 13f79535-47bb-0310-9956-ffa450edef68