title: Dispose of SWT shell when cursor moves out of it
body: <p>I'm implementing a custom preview/tooltip for an Eclipse plug-in. It did it using a Shell in SWT, removing all its trimmings and placing a text box inside it. It looks great. However now I need to dispose of the shell when the cursor moves out of the shell window and I ran into some issues: </p>
  
  <p>Does it make sense to attach a mousemoveListener to the shell? First I was doing this but then I realized that this listener only captures mouse move Events which occur inside the shell. How will I capture the mouse going out of the shell so as I could dispose of it?</p>
  
  <p>Thanks and regards,
  Krt_Malta</p>