Profiling of `git annex find --not --in web` suggests that converting Ref
to contain a ByteString, rather than a String, would eliminate a
fromRawFilePath that uses about 1% of runtime.

[[!tag confirmed]]

> Well, I did the conversion. Running that command does not seem to have 
> sped up by any appreciable amount. But, I did notice several places where
> using ByteString is certainly more efficient. It may just be that it
> doesn't matter if git-annex is IO bound etc. Still, glad I did it.
> [[done]] --[[Joey]]
