Tutorial 11 is missing a call to glfwPollEvents

```
If you do a diff between Tutorial 10 and 11 you'll see that the call to 
glfwPollEvents() is missing. This causes the app in tutorial 11 to not catch 
the Escape key in order to exit.

```

Original issue reported on code.google.com by `andrej.mitrovich` on 4 Mar 2014 at 9:15
