Merge of r1849174 from trunk:

  *) mod_md: incorrect behaviour when synchronizing ongoing ACME challenges
     have been fixed. [Michael Kaufmann, Stefan Eissing]



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1849176 13f79535-47bb-0310-9956-ffa450edef68