Add back the MonadException instance for mtl's StateT We don't actually use mtl's StateT anymore, but to follow the PVP we shouldn't remove this instance until the next major release.
Add back the MonadException instance for mtl's StateT
We don't actually use mtl's StateT anymore, but to follow the PVP we shouldn't
remove this instance until the next major release.

ghc/packages-haskeline,judah/haskeline,leroux/packages-haskeline,judah/haskeline,ghc/packages-haskeline