Print <undefined> in d8 when used as interactive shell.

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 120496eccce5921f887eafadf6ebd71e59867edc..6ce7cd1625d99b6dd6887e8f23fd678c332436ff 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -172,7 +172,10 @@ bool Shell::ExecuteString(Handle<String> source,
       return false;
     } else {
       ASSERT(!try_catch.HasCaught());
-      if (print_result && !result->IsUndefined()) {
+      if (!print_result) return true;
+      if (result->IsUndefined()) {
+        printf("<undefined>\n");
+      } else {
         // If all went well and the result wasn't undefined then print
         // the returned value.
         v8::String::Utf8Value str(result);