More GND + role inference woes

Ben Gamari was trying to update my linear package to work with GHC HEAD. Along the way he noted an example of the new GND+role inference machinery failing rather spectacularly. http://hackage.haskell.org/package/linear-1.3/docs/src/Linear-Affine.html#Po... Note the number of classes that the current proposal would force us to hand implement. =( -Edward