[MERGE] UTF-8 encoding in binary diffs

[Martin Pool]

Martin Pool has voted -0.
Status is now: Waiting
Comment:
I think changing to %s rather than %r is definitely right.

And I think encoding just the filename, rather than the whole stream, is 
also probably right, as it will give better results if we don't know the 
encoding of the contents of the file.

My only query is whether we should be hardcoding utf-8 here.  Shouldn't 
we be putting the filenames into the user's encoding?

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3Cd06a5cd30707090048l588e49c3wdfb8aaf3379f3b5e%40mail.gmail.com%3E