libgit2/git2go — pull request #150 by sqs (2014-12-09 22:13:00+00:00)
Title: Diff: heed DiffOptions fields OldPrefix and NewPrefix

This PR makes diffing heed the OldPrefix and NewPrefix fields in
DiffOptions.

Before this patch, running the modified TestDiffTreeToTree fails:

```
--- FAIL: TestDiffTreeToTree-12 (0.02s)
diff_test.go:150: Diff patch doesn't contain "x1/README" or "y1/README"

diff --git a/README b/README
index 257cc56..820734a 100644
--- a/README
+++ b/README
@@ -1 +1 @@
-foo
+file changed

```

It passes with the changes to diff.go in this PR.