patch applied (ghc-6.8/ghc): Finally, I managed to squash an infamous bug in :print

[Ian Lynagh]

Thu Sep 27 08:13:00 PDT 2007  Pepe Iborra <mnislaih at gmail.com>
  * Finally, I managed to squash an infamous bug in :print
    
    It turns out the newtype handling code in :print
    was slipping non mutable Tyvars in the types reconstructed.
    The error message eventually produced was rather obscure:
    
    [src/Tp.hs:75:28-64] *MainTp> :p x
    *** Exception: No match in record selector Var.tcTyVarDetails
    [src/Tp.hs:75:28-64] *MainTp>
    
    Due to non mutable tyvars, unifyType was failing.
    A well placed assertion in the unifyType code would have made
     my life much easier.
    Which reminds me I should install a -ddump-* system in the 
    RTTI subsystem, or future hackers will run away in swearing.
  
  
  MERGE TO STABLE
  

    M ./compiler/ghci/RtClosureInspect.hs -20 +28