lei_mail_sync: ensure URLs and folder names are stored as binary
Apparently leaving {sqlite_unicode} unset isn't enough, and
there's subtle differences where BLOBs are stored differently
than TEXT when dealing with binary data. We also want to avoid
odd cases where SQLite will attempt to treat a number-like value
as an integer.
This should avoid problems in case non-UTF-8 URLs and pathnames are
used. They'll automatically be upgraded if not, but downgrades
to older lei would cause duplicates to appear.