I didn't see how to get at these fields in the underlying git_diff_hunk, so I copied them into obj-c properties on GTDiffhunk. I'm not really sure if that's the right way to do it–if you'd prefer I pass through to the git_diff_hunk or if there's some other way that I'm missing.

I updated the hunk-related spec in GTDiffSpec.m because I didn't see any test files dedicated specifically to GTDiffHunk.