QuickCheck properties for IntSet

[Don Stewart]

dbenbenn:
> Here's a patch to IntSet.hs that adds many QuickCheck properties.  It
> adds properties testing almost all of the public interface of IntSet,
> and also properties testing that the data type invariants are never
> broken.  (The patch doesn't test the Data, Eq, Monoid, Read, or
> Typeable instances.)
> 
> Also, this patch removes a helper function, foldlStrict, and replaces
> it with calls to Data.List.foldl'.
> 
> I have two questions:
> 
> 1) Is this the right way to submit patches?

Thanks so much David, for taking the time to do this! Getting the
testing up to date on the somewhat-forgotten base code is really
important.

Ian, can we get these into the base library testsuite?

Have you tried getting some code coverage for you testsuite, btw? 
(Compile with -fhpc, and then run "hpc report" on the resulting .tix
file, to get numbers on how thorough the coverage is)


-- Don