goprotobuf: Use local imports for testdata package.

TBR=r
CC=golang-dev
http://codereview.appspot.com/5832043
diff --git a/proto/equal_test.go b/proto/equal_test.go
index 50b238f..af99c57 100644
--- a/proto/equal_test.go
+++ b/proto/equal_test.go
@@ -35,8 +35,8 @@
 	"log"
 	"testing"
 
+	pb "./testdata"
 	. "code.google.com/p/goprotobuf/proto"
-	pb "code.google.com/p/goprotobuf/proto/testdata"
 )
 
 // Four identical base messages.