Add retval opcode handler.

tests/jerry/N.function_return.js

@@ -0,0 +1,33 @@
+// 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.
+
+function f_empty()
+{
+  return;
+}
+
+function f_42()
+{
+  return 42;
+}
+
+function f_expr()
+{
+  var a = 5;
+  var b = 5;
+  return a + b;
+}
+
+assert(f_expr() === 10);
+assert(f_42() === 42);