Create a helper function "get_canned_error_string" for use by

ap_send_error_response.  The new function simply returns the error response
string corresponding to given HTTP error core.  This makes it easier to
change the mechanism for sending these strings, because we no longer have
r[v]puts calls spread throughout the error string generation code.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86341 13f79535-47bb-0310-9956-ffa450edef68