fix external_auth @ssl_login_shortcut decorator to properly use retfun
add missing retfun
remove @cache_if_anonymous
Added full test coverage for ssl login decorator
I also removed conflicting implementation of SSL_AUTH_IMMEDIATE_SIGNUP
and rebased on the current master.
Added comment as requested
Replaced retfun in ssl_login so that it properly redirect to dashboard
Merge pull request #1862 from carsongee/bugfix/mitx/external_auth-retfun

Fix external_auth to properly use retfun for @ssl_login_shortcut()