Add unary_plus and unary_minus opcodes

tests/jerry/unary_plus_minus.js

@@ -0,0 +1,18 @@
+// Copyright 2014 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.
+
+assert (+0 === -0);
+assert (1/-0 === -Infinity);
+assert (1/+0 === Infinity);
+assert ("3" -+-+-+ "1" + "1" / "3" * "6" + "2" === "42");