define gcd 0 0 = 0 (Ticket #3304)

As much as I'd love gcd 0 0 to be 0, the major problem is that this change would contradict the Haskell 98 report. Persumably the Haskell report needs to be changed first. Is there a ticket for this for Haskell prime? I didn't find one. -- Russell O'Connor http://r6.ca/ ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''