Backport:

mod_proxy_ajp: Really regard the operation a success, when the client
aborted the connection. In addition adjust the log message if the client
aborted the connection.
+1: rpluem, sf, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@917038 13f79535-47bb-0310-9956-ffa450edef68