Revert "Only save $_POST if no files have been uploaded"

This reverts commit ae240fbdb0a1075bb55af91b92dabfafe8f5e971.
Revert "Introduce a new login_redirect.php page the administrator is taken to when an administrator performs an action in an expired session. The POST contents are added to a hidden form on the page to re-submit the prior action performed."

This reverts commit 626b6a02855a8f977536a427c0f81416d670c19d.
Don't use the auth_user credentials if the administrator used the login form to enter a username and password
Don't show an invalid administrator message if auth_user is used