patches/diffs for full :browse! (fixes most of #1617)

[Claus Reinke]

>| however, you don't actually seem to do any lifting to merge
>| the two foralls in front, and still claim that
>|
>|     c :: forall a b. (C a b) => forall a1. a1 -> b
>|
>| is a valid type - ghc disagrees!-) nesting foralls is ok, but
>| nesting a forall in a context does not seem to be accepted.
>|
>| do you intend to change that (either the acceptance, or the
>| output), or should i send my updated patches now?
>
>I don't understand the issue here.  That really *is* the type 
>of c.  What do you mean that ghc "disagrees"?

simply that ghc neither accepts nor infers that type:

    $ cat T.hs
    {-# OPTIONS_GHC -fglasgow-exts #-}
    module Main where
    class C a b where c1 :: forall a. a -> b
    c :: forall a b. (C a b) => forall a1. a1 -> b
    c = undefined

    $ ghc T.hs
    
    T.hs:4:28: parse error on input `forall'

    -- comment out 'c', then
    $ ghc -fglasgow-exts -e ':t c1' T.hs
    c1 :: forall a a1 b. (C a b) => a1 -> b

i understand that the type given by printTyThing should
be equivalent to the one ghc likes to parser and infer,
but ghc doesn't seem to accept them as equivalent.

claus