I just had to set that variable you referenced up on our installation, because links from emails etc were presenting the old login page, and the button we added to take people to shibboleth was losing the 'this is the moodle URL I want' parameter in IE (Chrome was fine).
I will start a new thread asking how we enable manual login for admin - otherwise I have suggested disabling the alternatelogin parameter, going in as admin and assigning the Administrator system role to the network IDs of those who need it.