[plt-scheme] plt web server leak

You may recall the recent messages concerning an apparent memory leak 
in the plt web server. After a couple of days of investigating this 
problem, it turns out that there is no memory leak in the server. 
Instead, the server allocates a lot of memory per servlet and servlet 
suspension, and as a result, a heavy load on the server quickly 
consumes the memory when no connection ever completes the interaction 
chain. The problem is mostly due to (1) a relatively naive resource 
management strategy in the server -- we use only time-outs to control a 
servlet's life span -- and (2) a few structural flaws in the language. 
We are investigating (1), which is the larger factor, and hope to come 
up with alternatives soon.

-- Matthias