Optimize _.isEmpty. [closes #1888]

lodash.js

@@ -9550,9 +9550,16 @@
      * // => false
      */
     function isEmpty(value) {
-      return (!isObjectLike(value) || isFunction(value.splice))
-        ? !size(value)
-        : !keys(value).length;
+      if (isArrayLike(value) &&
+          (isArray(value) || isString(value) || isArguments(value) || isFunction(value.splice))) {
+        return !value.length;
+      }
+      for (var key in value) {
+        if (hasOwnProperty.call(value, key)) {
+          return false;
+        }
+      }
+      return true;
     }
 
     /**