Fix for Issue #70 - EquivalentTo isn't compatible with Ignorecase for dictionaries

I decided the IgnoreCase should apply to both characters and strings for any equality comparison. It had only applied to strings. The root of the problem was actually below the tally and in the NUnitEqualityComparer as it did not support generic dictionaries or characters. It also did not support equality of Dictionaries where we ignore the case of the key.

To test this issue, I added tests to

CollectionEqualsTest
CollectionContainsConstraintTest
CollectionEquivalentContraintTest
UniqueItemsConstraintTest

To be more explicit, I might want to add some additional tests to NUnitEqualityComparerTests, but I believe it gets a better workout at the higher level.