Two entire days spent making a branch where git-annex uses ByteString
instead of String, especially for filepaths. I commented out all the
commands except for find, but it still took thousands of lines of patches
to get it to compile.

The result: git-annex find is between 28% and 66% faster when using
ByteString. The files just fly by!

It's going to be a long, long road to finish this, but it's good to have a
start, and know it will be worth it.
[[todo/optimize_by_converting_String_to_ByteString]] is the tracking page
for this going forward.