Convert log_*() to aplog_error().

Something needs to be done with proxy_log_uerror() in here. I see no obvious
reason not to replace it with aplog_error() but would like some feedback first.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@79133 13f79535-47bb-0310-9956-ffa450edef68