Parse error on unparenthesized nested foralls

[int-index]

Test case:

incu :: () -> forall a. Num a => a -> a
incu _ x = x + 1

main = print (incu () 41)

Expected behavior (ghc used as reference)

$ runhaskell Test.hs  
42

Actual behavior (mhs)

$ ./bin/mhs -r Test.hs

mhs: uncaught exception: error: "Test.hs": line 1, col 15:
  found:    forall
  expected: LQIdent ( UQIdent [ literal

Adding parentheses results in #208, but it seems to be a separate issue from the parse error.