Git think some of .cs files are binary because they use "UCS-2 Little Endian"(according to Notepad++):

If I convert file to UTF8 git applications start displaying this files as text file(diff works).
Without this change pull requests look like this: https://github.com/dotnet/roslyn/pull/65/files

I think some tool should be used to convert all files to UTF8.