Let’s say we set session[:foo] = ‘bar’. Now we want to remove the :foo
key completely. How do you do that?
Appearantly, session is a CGI::Session  instance, so it doesn’t
have #delete like Hash. I tried:
session[:foo] = nil
But then debug(session) shows an empty :foo key. I’d like to remove
that key, as my session is already pretty crowded. Is it possible?