User_login form should have a federated link

Previous patch did not apply due to unreliable file path.

I've created a 7.x-3.x branch of this module with significant refactoring. It includes patches from the following issues:

#2190487: User_login form should have a federated link
#2213283: When simplesamlphp_auth_activate is 0 watchdog messages flood the syslog/dblog
#2221679: Destruction of session causes fatal error
#2020009: Session cookie being set, breaking through Varnish cache.
#1824194: hook_user_insert issues when user adding a new user is logged in via sso
#2205901: Allow SimpleSAML authentication on a per-user basis

https://github.com/grasmash/simplesamlphp_auth/tree/7.x-3.x

Given that so much work has been done (and it will not cleanly merge with 7.x-2.x) I propose that a new 7.x-3.x-dev branch be added to the module.

Committed to 3.x