title: Qt : Tooltip on wrong input
body: <p>I have a QLineEdit, on which I have set a QRegExpValidator, that allows the user to input only one whitespace between words.<br>
  Now I want that whenever the user tries to enter more than one whitespaces, the tooltip of the QLineEdit should show up, but I'm not getting any method to implement it.</p>
  
  <p>Thanx :)</p>