were present due to things being allocated, and structures being
zeroed every time through the redirect loop instead of per-request.

Changes include:
 Add new request finished BOOL (session.req.finished) indicating that
a close_request() should follow.
 Move close_request() calls into http_session_thread()
 Check that lists aren't already initialized
 Fix up memory leaks in logging
 Send a 500 error if strListInit() fails (Not related to redirect
looping)