swap minView/maxView return value.

[Jean-Philippe Bernardy]

Some time ago (before ghc 6.6 / base 2.0 release), I introduced
minView and maxView in Data.Set and Data.Map (at a user's request). I
agreed with Robert Dockins to implement the same functionality as in
his version of the Edison library. Unfortunately, I uselessly swapped
the return values of minView and maxView, introducing a difference
both with the corresponding functions in the edison library and
similar functions in Data.Map/Set.

I propose to restore the symmetry, at the cost of incompatibility.
The incompatibility is probably acceptable because the functions are
still short-lived.

See the trac ticket for details.
http://hackage.haskell.org/trac/ghc/ticket/1134

I provide no patch nor QuickCheck properties because of the triviality
of the change.

Cheers,
JP.