Add the UseCanonicalName directive which controls how self-referential

Add the UseCanonicalName directive which controls how self-referential
redirects are generated.  This was at least approved in spirit by a
handful of folks two weeks ago.  The default should be no behaviour
change.

This changes the prototype of construct_url(), and adds two new
API functions: get_server_name() and get_server_port().  So the
MODULE_MAGIC_NUMBER has been bumped.

PR:             315, 459, 485, 1433
Submitted by:   Michael Douglass <mikedoug@texas.net>, Dean Gaudet

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@80076 13f79535-47bb-0310-9956-ffa450edef68