Enhance the "unknown directive" error message to indicate some

	reasons *why* it might be invalid.

PR:		1479, 1480, and lots of others
Reviewed by:	Dean Gaudet, Martin Kraemer


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@79656 13f79535-47bb-0310-9956-ffa450edef68