Correctly enumerate function property members.

Functions has several built-in non-enumerable properties, and
they are correctly ignored during enumeration after this patch.

External function prototype is also lazy enumerated.

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

tests/jerry/es2015/function-properties.js

@@ -0,0 +1,46 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// 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 getProperties(obj)
+{
+  var str = "";
+  for (name in obj)
+  {
+    if (str)
+    {
+      str += " " + name;
+    }
+    else
+    {
+      str = name;
+    }
+  }
+  return str;
+}
+
+var prototype_obj = { dummy:1, length:1, caller:null,
+                      arguments:null, prototype:null };
+
+var func = function() {};
+
+Object.setPrototypeOf(func, prototype_obj);
+assert(getProperties(func) == "dummy caller arguments");
+
+var bound_func = (function() {}).bind(null);
+Object.setPrototypeOf(bound_func, prototype_obj);
+assert(getProperties(bound_func) == "dummy prototype");
+
+// 'print' is an external function
+Object.setPrototypeOf(print, prototype_obj);
+assert(getProperties(print) == "dummy length caller arguments");