• Disabling retries on "GET as POST" requests as that leads to undefined behaviour. See +232.
• Trying to read certificates from a "test/plain" response as well, since some
  servers seem to use that (see #232).
• Synchronized with Apache trunk. Spelling fixes and an added check when unsuccessfully
  reading JSON files.
• Fixed a theoretical uninitialized read when testing for JSON error responses from the
  ACME CA. Bugreported at https://bz.apache.org/bugzilla/show_bug.cgi?id=64297.