Merge /httpd/httpd/trunk:r1910996,1911721

Merge /httpd/httpd/trunk:r1910996,1911721

 * mod_md:
   - New directive `MDMatchNames all|servernames` to allow more control over how
     MDomains are matched to VirtualHosts.
   - New directive `MDChallengeDns01Version`. Setting this to `2` will provide
     the command also with the challenge value on `teardown` invocation. In version
     1, the default, only the `setup` invocation gets this parameter.
     Refs #312. Thanks to @domrim for the idea.
   - For Managed Domain in "manual" mode, the checks if all used ServerName and
     ServerAlias are part of the MDomain now reports a warning instead of an error
     (AH10040) when not all names are present.
   - MDChallengeDns01 can now be configured for individual domains.
     Using PR from Jérôme Billiras (@bilhackmac) and adding test case and fixing proper working
   - Fixed a bug found by Jérôme Billiras (@bilhackmac) that caused the challenge
     teardown not being invoked as it should.

 * mod_md: fixed passing of the server environment variables to programs
   started via MDMessageCmd and MDChallengeDns01 on *nix system.
   See <https://github.com/icing/mod_md/issues/319>.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1911722 13f79535-47bb-0310-9956-ffa450edef68