CLASSICWEB_OVERRIDE allows you to install an emulab that presents the classic UI as the default while still having the new apt UI enabled. This will assist with transitions as both UIs can be provided by the same instance of emulab. Admins and early adopters can gain experience with the new UI while the classic UI can be the default for normal users.
To make this work, we have to be careful not to unexpectedly redirect classic users to the new UI. This patch handles this case in some additional instances.