patch applied (ghc): Fix Trac #1759: do not let ticks get in the way of spotting trivially-true guards

[Simon Peyton Jones]

Wed Oct 10 09:47:31 PDT 2007  simonpj at microsoft.com
  * Fix Trac #1759: do not let ticks get in the way of spotting trivially-true guards
  
  GHC spots that an 'otherwise' guard is true, and uses that knowledge to 
  avoid reporting spurious missing-pattern or overlaps with -Wall.
  
  The HPC ticks were disguising the 'otherwise', which led to this failure.
  Now we check.  The key change is defining DsGRHSs.isTrueLHsExpr.
  
  Test is ds062
  
  

    M ./compiler/deSugar/DsGRHSs.lhs -4 +15