Mike Fleetwood authored Aug 29, 2012 and Curtis Gedak committed Aug 30, 2012

Steps to reproduce:
1) Open any of these dialogs: Create New Partition, Resize/Move or
   Paste;
2) Update any of the following numeric entry fields to a different value
   using the keyboard: Free space preceding, New size or Free space
   following;
3) Press [Esc] key;
Gparted crashes.

What is happening is that the [Esc] key is leading to the dialog being
closed and calling the ~Dialog_Base_Partition() destructor.  However
after this the GTK widget is calling the on_spinbutton_value_change()
registered callbacks for the change to the other two values, on the now
just deleted object.

Fix by disconnecting the change notification callbacks in the
destructor.

Closes bug #682658 - GParted crash by pressing Esc in dialogs with
                     number entry