Today I was indeed able to get to the bottom of and fix the bug that
had stumped me the other day.

Rest of the day was taken up by catching up to some bug requests and
suggestions for v6 mode. Like making unlock and lock work for files
that are not locally present. And, improving the behavior of the clean
filter so it remembers what backend was used for a file before and
continues using that same backend.

About ready to make a release, but IIRC there's one remaining test suite
failure on FAT.
