Yesterday, worked on cleaning up the todo list. Fixed Windows slash problem
with rsync remotes. Today, more Windows work; it turns out to have been
quite buggy in its handling of non-ASCII characters in filenames. Encoding
stuff is never easy for me, but I eventually managed to find a way to fix
that, although I think there are other filename encoding problems lurking
in git-annex on Windows still to be dealt with.

Implemented an interesting metadata feature yesterday. It turns out that
metadata can have metadata. Particularly, it can be useful to know when a
field was last set. That was already beeing tracked, internally (to make
union merging work), so I was able to quite cheaply expose it as
"$field-lastchanged" metadata that can be used like any other metadata.

I've been thinking about how to implement [[todo/required_content]]
expressions, and think I have a reasonably good handle on it.
