InResponseTo SubjectConfirmation validation support
Fix JSHint failures, implement CacheProvider the SAML object uses, provide in-memory default implementation
Merge branch 'assertion-inresponseto' of https://github.com/mradamlacey/passport-saml
Clean up the cache provider interface a little, and make sure the saml code also checks the expiration time so that if a cache provider doesn't flush expired tokens promptly, they'll still be invalid once the expiration interval elapses.