Fix concatenating of surrogates.

JerryScript-DCO-1.0-Signed-off-by: Andrey Shitov a.shitov@samsung.com

tests/jerry/string-surrogates-concat.js

@@ -0,0 +1,23 @@
+// Copyright 2015 Samsung Electronics Co., Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+var str0 = "𐐀";
+var str1 = "\ud801\udc00";
+var str2 = "\ud801";
+var str3 = "\udc00";
+
+var str_concat = str2 + str3;
+
+assert(str0 == str_concat);
+assert(str1 == str_concat);