patch applied (ghc): Semi-tagging optimisation

[Simon Marlow]

Mon Jan 22 03:40:16 PST 2007  Simon Marlow <simonmar at microsoft.com>
  * Semi-tagging optimisation
  In the generated code for case-of-variable, test the tag of the
  scrutinee closure and only enter if it is unevaluated.  Also turn
  *off* vectored returns.

    M ./compiler/codeGen/CgCallConv.hs -3 +4
    M ./compiler/codeGen/CgCase.lhs -12 +87
    M ./compiler/codeGen/CgInfoTbls.hs -1 +1
    M ./compiler/codeGen/CgTailCall.lhs -1 +1
    M ./compiler/codeGen/CgUtils.hs +3