patch applied (packages/base): make Data.Graph portable (no change to the interface)

[Ross Paterson]

Tue Nov 21 17:00:40 PST 2006  Ross Paterson <ross at soi.city.ac.uk>
  * make Data.Graph portable (no change to the interface)
  
  The algorithm now uses STArrays on GHC and IntSets elsewhere.
  (Hugs has STArrays, but avoiding them saves a -98, and boxed arrays
  aren't fast under Hugs anyway.)

    M ./Data/Graph.hs -23 +62