Quotes cannot be used around require group and require dn

directives, update the documentation to reflect this. Also add
quotes around the dn and group within debug messages, to make it
more obvious why authentication is failing if quotes are used in
error.
PR: 19304
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git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@103711 13f79535-47bb-0310-9956-ffa450edef68