On the trunk:

mod_md: eliminating compiler warnings re signedness and unused. Adding a APLOG_WARNING 
	when the only available ACME challenge is "tls-sni-01" since Let's Encrypt will
        disable that completely beginning of 2019.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1843543 13f79535-47bb-0310-9956-ffa450edef68