contextMenu always visible in window

When i will show the contextMenu that height and position of click is greater than window height a part of the contextmenu is hidden because it will show the contextMenu above the position of click.
Example
![contextmenu](https://cloud.githubusercontent.com/assets/3445672/2801032/d86a4698-cc7c-11e3-89b5-86af9ee9b013.png)