Merge r1725106 from trunk:

clarify a butchered sentence about missing ServerName, which
is a regular early step in "my directive didn't do anything".

This describes ap_get_local_host()



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1725108 13f79535-47bb-0310-9956-ffa450edef68