omit non-enumerable properties from cloned objects (#784)

Drastically improves performance in some cases (for example, when using the `--explain`/`-X` option).

lib/jsdoc/util/doop.js

@@ -1,7 +1,7 @@
 /*global Set */
 
 /**
-    Deep clone a simple object.
+    Deep clone a simple object. Ignores non-enumerable properties.
     @private
  */
 'use strict';
@@ -53,7 +53,7 @@ function doop(o, seen) {
             }
             else {
                 clone = Object.create( Object.getPrototypeOf(o) );
-                props = Object.getOwnPropertyNames(o);
+                props = Object.keys(o);
                 for (i = 0, l = props.length; i < l; i++) {
                     descriptor = Object.getOwnPropertyDescriptor(o, props[i]);
                     if (descriptor.value) {

test/specs/jsdoc/util/doop.js

@@ -1,4 +1,6 @@
 /*global describe, expect, it */
+'use strict';
+
 describe('jsdoc/util/doop', function() {
     var doop = require('jsdoc/util/doop');
 
@@ -77,6 +79,19 @@ describe('jsdoc/util/doop', function() {
             compareForEquality(inp, out);
         });
 
+        it('should not clone non-enumerable properties', function() {
+            var clone;
+            var obj = { a: 1 };
+
+            Object.defineProperty(obj, 'foo', {
+                value: 2
+            });
+
+            clone = doop(obj);
+
+            expect(clone.foo).not.toBeDefined();
+        });
+
         it('should not create a circular reference if an object is seen more than once', function() {
             var input = { a: {} };
             var output;