[Gecode] ViewTuple instead of ViewPair

[Christian Schulte]

Please,

could everybody using ViewPair<View> convert to ViewTuple<View,2>? Then
ViewPair can be removed. This is actually the last interface change before
the release (as far as I can see).

ViewPair is only used in sortedness. Maybe one now can use ViewTuple<View,3>
altogether there?

Christian

--
Christian Schulte, http://www.imit.kth.se/~schulte/