Just wanted to let everyone know that I've made some changes to the session handling code. Because of search history-related cleanup introduced by the Search Object, it is no longer possible to rely on PHP's built-in handlers for sessions. I've moved more shared logic into the base SessionInterface class, and I have expanded and adjusted the MemcacheSession and MySQLSession classes to make use of this logic. I've also added a new FileSession class to allow file-based sessions as a third option, and I've expanded documentation and available settings in config.ini to make this easier to configure.
I've tested all three session methods locally and they seem to be working -- please take a look at r1736 and let me know if you have any questions or problems.