patch applied (ghc): Teach cheapEqExpr about casts

[Roman Leshchinskiy]

Tue Feb  5 19:50:07 PST 2008  Roman Leshchinskiy <rl at cse.unsw.edu.au>
  * Teach cheapEqExpr about casts
  
  Previously, cheapEqExpr would always return False if it encountered a cast.
  This was bad for two reasons. Firstly, CSE (which uses cheapEqExpr to compare
  expressions) never eliminated expressions which contained casts and secondly,
  it was inconsistent with exprIsBig. This patch fixes this.

    M ./compiler/coreSyn/CoreUtils.lhs -1 +4
    M ./compiler/types/Coercion.lhs +9