Slightly modified the API to allow handlers by things other than

content type. Setting r->handler will override r->content_type in
invoke_handler().

Reviewed by: Ben Laurie, Randy Terbush


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@76358 13f79535-47bb-0310-9956-ffa450edef68