CDC 6.16.6

mkalkbrenner: fixed page_cache_max_age. see https://bugs.launchpad.net/pressflow/+bug/575754/comments/4 mkalkbrenner: If no cache_lifetime is set, pages are always CACHE_TEMPORARY. In this case it's more efficient to truncate the cache in cache_clear_all() mkalkbrenner: Added performance debug tools: Memory Threshold and Session Starter