patch applied (ghc): Check for escape when unifying forall-types

[Simon Peyton Jones]

Tue Feb  6 08:54:56 PST 2007  simonpj at microsoft.com
  * Check for escape when unifying forall-types
  
  This egregious omission led to Trac #1128.
  

    M ./compiler/typecheck/TcUnify.lhs -6 +22