Diff patch (#3345)

* Add support for .diff and .patch

Add the ability to get text-diff and format-patch by adding .diff or
.patch in the end of a commit url. Issue #2641

* models: git_diff: various fixes

* Renames commitId to commitID.
* Writes stderr to a bytes.Buffer and displays proper error message on
command failure.
* Various style changes.

Signed-off-by: Dennis Chen <barracks510@gmail.com>

routers/repo/commit.go

@@ -195,7 +195,16 @@ func Diff(ctx *context.Context) {
 }
 
 func RawDiff(ctx *context.Context) {
-	panic("not implemented")
+	diff, err := models.GetRawDiff(
+		models.RepoPath(ctx.Repo.Owner.Name, ctx.Repo.Repository.Name),
+		ctx.Params(":sha"),
+		ctx.Params(":ext"),
+	)
+	if err != nil {
+		ctx.Handle(404, "GetRawDiff", err)
+		return
+	}
+	ctx.HandleText(200, diff)
 }
 
 func CompareDiff(ctx *context.Context) {