change r.content_type = "something" to use ap_set_content_type, which it...

change r.content_type = "something" to use ap_set_content_type, which it should as was pointed out by Bertrand Mansion

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@748946 13f79535-47bb-0310-9956-ffa450edef68