[plt-scheme] correctness of capturing continuations in servlets

Hi Alexander,

This is a tricky problem.  Basically you need to have some notion of
transactional support built into the programming language, and then
hae the run-time system support this.  A student and I expect to be
looking into this topic this summer.  (DYNAMIC-WIND may prove to be
critical for implementing this.)

For now, however, we don't have a good story on this, but neither do
the other research systems -- though notably Mawl prevents back-button
access due to its inability to guarantee behavior in these situations.

Shriram