Fixed two difficult bugs with direct mode. One happened (sometimes) when a
file was deleted and replaced with a directory by the same name and then
those changes were merged into a direct mode repository.

The other problem was that direct mode did not prevent writes to
.git/annex/objects the way that indirect mode does, so when a file in the
repository was not currently present, writing to the dangling symlink would
follow it and write into the object directory.

Hmm, I was going to say that it's a pity that direct mode still has so many
bugs being found and fixed, but the last real bug fix to direct mode was
made last May! Instead, I probably have to thank Tim for being a very
thorough tester.

Finished switching the test suite to use the tasty framework, and prepared
tasty packages for Debian.
