patch applied (hugs98): report the top-level goal when hitting the cutoff (fixes #65)

[Ross Paterson]

Fri Apr 20 13:28:47 PDT 2007  Ross Paterson <ross at soi.city.ac.uk>
  * report the top-level goal when hitting the cutoff (fixes #65)
  
  Formerly cutoffExceeded() reported the current goal, which was not
  necessarily part of the problematic cycle.  For example, given
  
      class C a where
          f :: a -> a
  
      instance (Eq a, C a) => C a
  
      test = f True
  
  it reported that it could not prove Eq Bool, even though this is
  provable in one step.

    M ./src/preds.c -6 +22