Ensure _.attempt preserves custom errors.

lodash.js

@@ -12926,7 +12926,7 @@
       try {
         return apply(func, undefined, args);
       } catch (e) {
-        return isError(e) ? e : new Error(e);
+        return isObject(e) ? e : new Error(e);
       }
     });
 

test/test.js

@@ -1482,6 +1482,20 @@
       assert.ok(lodashStable.isEqual(actual, Error('x')));
     });
 
+    QUnit.test('should preserve custom errors', function(assert) {
+      assert.expect(1);
+
+      function CustomError(message) {
+        this.name = 'CustomError';
+        this.message = message;
+      }
+
+      CustomError.prototype = lodashStable.create(Error.prototype);
+
+      var actual = _.attempt(function() { throw new CustomError('x'); });
+      assert.ok(actual instanceof CustomError);
+    });
+
     QUnit.test('should work with an error object from another realm', function(assert) {
       assert.expect(1);