saml2/SSOService: Handle exceptions.
saml2/SSOService: Handle exceptions.

This patch uses the recently added infrastructure for passing
exceptions from authentication modules and filters. Exceptions
will be passed to the service provider.

Rud5G/simplesamlphp,Rud5G/simplesamlphp,Rud5G/simplesamlphp,Rud5G/simplesamlphp