Fixing the order that labeled fields appear in datatypes. Currently
they are reversed, which breaks the prelude badly.

[From Haskell report:

The arguments to the positional constructor occur in the same order as the labeled fields. For example, the declaration

  data C = F { f1,f2 :: Int, f3 :: Bool}

defines a type and constructor identical to the one produced by

  data C = F Int Int Bool

]