Registry path fix

Git for Windows can add `<Git Folder>/cmd` to the PATH, but msysgit_in_path() expects just `<Git Folder>/bin`.
https://github.com/msysgit/msysgit/blob/master/share/WinGit/install.iss#L1062

This is probably only crucial when you are debugging the dll outside of the git-cheetah folder, having registered it from there, because the only way to get the extension to run is to correct the path in the registry.