arrow notation: incorrect scope of existential dictionaries

ghc-6.4: panic! (the `impossible' happened, GHC version
6.4):
        cgPanic
    deref{v a1yz}
    static binds for:
    local binds for:
    SRT labelghc-6.4: panic! (the `impossible'
happened, GHC version 6.4):
        initC: srt

Please report it as a compiler bug to
glasgow-haskell-bugs@haskell.org,
or http://sourceforge.net/projects/ghc/.

I've attached a test driver that can reproduce the problem.

-- Esa Pulkkinen <esa.pulkkinen@kotiposti.net>