Undo: use dive * instead of unique index in renumber-dives

Now, that pointers to dives are stable, we might just as well
use dive * instead of the unique-id. This also affects the
merge-dive command, as this uses the same renumbering machinery.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

desktop-widgets/command.cpp

@@ -21,7 +21,7 @@ void shiftTime(const QVector<dive *> &changedDives, int amount)
 	execute(new ShiftTime(changedDives, amount));
 }
 
-void renumberDives(const QVector<QPair<int, int>> &divesToRenumber)
+void renumberDives(const QVector<QPair<dive *, int>> &divesToRenumber)
 {
 	execute(new RenumberDives(divesToRenumber));
 }