Folder-based searching

[Sebastian Spaeth]

> Before the next release, I plan to increment the database version so
> that users will be notified of the need to do an upgrade like this. (But
> before I do that, I plan to implement a few more database changes---and
> some of them are likely to be much more invasive than this one).

Hurray, just tried it out and it works like a charm. Finally I can
automatically assign the "Junk" tag again. :-)

Sebastian