Extend the supported environment sizes of vectorised closures

ghc: panic! (the 'impossible' happened)
  (GHC version 7.2.1 for i386-apple-darwin):
	VectMonad.lookupFamInst: not found: 
    dph-par:Data.Array.Parallel.PArray.PData.PData{tc r4u}
      (ghc-prim:GHC.Types.Int{(w) tc 3J},
       ghc-prim:GHC.Types.Int{(w) tc 3J},
       dph-par:Data.Array.Parallel.PArray.Base.PArray{tc r1}
         (ghc-prim:GHC.Types.Int{(w) tc 3J},
          ghc-prim:GHC.Types.Int{(w) tc 3J},
          ghc-prim:GHC.Types.Double{(w) tc 3u}),
       ghc-prim:GHC.Types.Int{(w) tc 3J},
       ghc-prim:GHC.Types.Int{(w) tc 3J}
       dph-par:Data.Array.Parallel.Lifted.Closure.:->{tc r2} (ghc-prim:GHC.Types.Int{(w) tc 3J}
                                                              dph-par:Data.Array.Parallel.Lifted.Closure.:->{tc r2} ghc-prim:GHC.Types.Int{(w) tc 3J}),
       ghc-prim:GHC.Types.Int{(w) tc 3J})

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug