Allow debug trace info to extend across redirects

[scorfield]

This would require caching the trace information in session scope but that makes it tough to be thread safe (multiple threads really still need their own trace). It's also a problem for apps with session management turned off (you get an exception every time you say "session" even inside isDefined() which will tick ppl off).

I had a stab at this for 5.1 but it was too complex so I reverted the changes (see changesets [316] [317] and [318] for the timeframe on the code base).

Opening a ticket for consideration for 6.0.

[scorfield]

Defer to 5.6 to figure out proper solution.