Fixes span bug by also update span on removal of high
Expands test cases
Fixes a comment
Removes unused classes for code contracts on IList and IDictionary
Adds some commented out code contracts along with some more fixed seed tests
Fixes an error in the use of HashBag that gave problems with the code contract. The problem might still be there when using Choose on HashBags!
Adds a test interval for black box tests, which has a random id to make it easier to identify reference equal objects during testing.