rewrite rule pragma syntax

[Henning Thielemann]

I encountered the same problem as this guy:
 http://www.haskell.org/pipermail/glasgow-haskell-users/2002-May/003407.html

It is still present in GHC-6.2.1. Only if you turn on -fglasgow-exts the
RULES pragma is parsed correctly. I think GHC should give a warning like
"turn -fglasgow-exts on for RULES pragma" instead of: 

Media.hs:23: Variable not in scope: `forall'

Media.hs:23: Variable not in scope: `f'

Media.hs:23: Variable not in scope: `f'

Media.hs:23: Variable not in scope: `f'