Generalize default_port manipulations.

The proxy may still need some work, but will defer until I can
review these changes with others.
Obtained from: Ben Laurie, Randy Terbush
Reviewed by: Ben Laurie, Randy Terbush


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@80080 13f79535-47bb-0310-9956-ffa450edef68