"precedence when printing context" patch breaks ghc-7.8 branch

[Jost Berthold]

Hi,

A build of the ghc-7.8 branch in its current state failed for me today 
in compiler/types/TypeRep.lhs

I am at commit 7b1d4c4 ("release note blurb..."), there was only one 
more since ("revert 'revert'...").

It seems as though the merge of commit d71f316ef ("...precedence when 
printing contexts..") does not fit into ghc-7.8 (that patch works on 
HEAD, of course). Error message is:

compiler/types/TypeRep.lhs:540:35:
     Not in scope: data constructor `TyOpPrec'

(a constructor introduced by that patch)

I have no idea how to fix this (GHC itself suggests "TopPrec", but that 
actually reverts the fix :-) )

Cheers,
Jost Berthold