Fix checkdiff on windows

This attempts to fix issue #13.

I've removed single quotes from pretty formatting, because they seem to be causing this problem in `git diff`. As it seems the quotes are unnecessary when comparing two commit hashes both on Windows and *nix systems.

I've also refactored reading of the remote .rev file, since it's always coming as raw binary data.

Please feel free to criticize and reject this for whatever reason.