patch: handle text diffs from git

R=r
CC=golang-dev
https://golang.org/cl/194094

src/pkg/patch/patch.go

@@ -207,7 +207,7 @@ func Parse(text []byte) (*Set, os.Error) {
 				p.Diff = diff
 				break
 			}
-			if hasPrefix(l, "index ") || hasPrefix(l, "GIT binary patch") {
+			if hasPrefix(l, "GIT binary patch") || (hasPrefix(l, "index ") && !hasPrefix(raw, "--- ")) {
 				diff, err := ParseGitBinary(oldraw)
 				if err != nil {
 					return nil, err
@@ -215,6 +215,9 @@ func Parse(text []byte) (*Set, os.Error) {
 				p.Diff = diff
 				break
 			}
+			if hasPrefix(l, "index ") {
+				continue
+			}
 			return nil, SyntaxError("unexpected patch header line: " + string(l))
 		}
 		if p.Diff == nil {

src/pkg/patch/patch_test.go

@@ -50,6 +50,17 @@ var tests = []Test{
 			"-hello, world\n" +
 			"+goodbye, world\n",
 	},
+	Test{
+		"hello, world\n",
+		"goodbye, world\n",
+		"Index: a\n" +
+			"index cb34d9b1743b7c410fa750be8a58eb355987110b..0a01764bc1b2fd29da317f72208f462ad342400f\n" +
+			"--- a/a\n" +
+			"+++ b/b\n" +
+			"@@ -1 +1 @@\n" +
+			"-hello, world\n" +
+			"+goodbye, world\n",
+	},
 	Test{
 		"hello, world\n",
 		"goodbye, world\n",