title: Are signals in Qt automatically disconnected when one of the class is deleted
body: <p>Does Qt automatically remove connections between objects , when one of the side is deleted ?</p>
  
  <p>e.g <code>connect (A .. , B ..)</code> , when A (a pointer) is deleted , or B is deleted , will the connection be disconnected ? </p>
  
  <p>Is it necessary to use disconnect explicitly in destructor ?</p>