More back-end shenanigans!

Log file handling should be a lot more sturdy now. Moving a session from one category to another should move its file along with it, and the freak corner cases are handled better now. Really, there are surprisingly many of those, my code reveals; I'd forgotten half of them, yet they're all sane! Example: changing a piece of news from type 'log' to type 'ic', which completely destroys the log file.

Some of that was thankfully made possible by the whole zip-fix shenanigans, since the zip generator can now handle things the report script used to handle for it. Or tried to handle for it, and failed miserably.