Previously, we were taking folder names as they came off the wire.
Turns out IMAP specifies that folder names with 8 bit code points are
encoded in a crazy scheme unique to IMAP. Now, we properly decode that
scheme to the correct UTF-8 folder names to be displayed to the user.
There's also now a database upgrade path that converts all existing
mailboxes to the decoded version, so your existing database should just
keep working.
