fixes #992: simplifies clear_session_user.  works in conjunction with an apache config change: adding RequestHeader unset REMOTE_USER above CoSign directives.  tested on -test instance
fixes #992: simplifies clear_session_user.  works in conjunction with an apache config change: adding RequestHeader unset REMOTE_USER above CoSign directives.  tested on -test instance

jeremyf/sufia,ndlib/scholarsphere,ndlib/scholarsphere,samvera/hyrax,zhang4952/scholarsphere,samvera/hyrax,samvera/hyrax,ndlib/scholarsphere,zhang4952/scholarsphere,samvera/hyrax,zhang4952/scholarsphere,jeremyf/sufia,zhang4952/scholarsphere