Merged /httpd/httpd/trunk:r1869392

Merged /httpd/httpd/trunk:r1869392

  *) mod_md v2.2.3:
     - Configuring MDCAChallenges replaces any previous existing challenge configuration. It
       had been additive before which was not the intended behaviour. [@mkauf]
     - Fixing order of ACME challenges used when nothing else configured. Code now behaves as
       documented for `MDCAChallenges`. Fixes #156. Thanks again to @mkauf for finding this.
     - Fixing a potential, low memory null pointer dereference [thanks to @uhliarik].
     - Fixing an incompatibility with a change in libcurl v7.66.0 that added unwanted
       "transfer-encoding" to POST requests. This failed in directy communication with
       Let's Encrypt boulder server. Thanks to @mkauf for finding and fixing. [Stefan Eissing]

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1869394 13f79535-47bb-0310-9956-ffa450edef68