This also helps us manage checking, case-insensitive, for
subscriptions while preserving the casing used by the class creator
for display.
It also fixes a bug where the class_list would become out of sync with
your true subscriptions, allowing you to appear to send messages to
classes to which you had unsubscribed.
(imported from commit 5e8d017bcfb27a71c52f7517733eda7b926d721b)
