mod_auth_form: Support the expr parser in the

AuthFormLoginRequiredLocation, AuthFormLoginSuccessLocation
and AuthFormLogoutLocation directives.

mod_auth_form: Make sure 500 Internal Server Error is
returned should an error occur while parsing an expression.

Submitted by: minfrin
Backported by: minfrin
Reviewed by: minfrin, sf, rjung

Backports of r1388648 and r1418721 from trunk.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1420071 13f79535-47bb-0310-9956-ffa450edef68