Merge r1531672 from trunk:

mod_auth_form: Make sure the optional functions are loaded even when
the AuthFormProvider isn't specified.

Submitted by: minfrin
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1588247 13f79535-47bb-0310-9956-ffa450edef68