In a v6 repository on a filesystem not supporting symlinks,
it makes sense for commands like `git annex add` and `git annex import`
to add the files unlocked, since locked files are not usable there.
After implementing that, I also added an `annex.addunlocked` config setting,
so that the same behavior can be configured in other repositories.

Rest of the day was spent fixing up the test suite's v6 repository tests
to work on FAT and Windows.