saml: Add support for SAML 1.1 IdP init SSO.
saml: Add support for SAML 1.1 IdP init SSO.

Some limitations apply. Specifically, no support for the Artifact
binding, and the TARGET parameter must be an absolute url.

rchavik/simplesamlphp,rchavik/simplesamlphp,rchavik/simplesamlphp,rchavik/simplesamlphp