IntVar unit tests! Lots and lots of them!

Also, fixed stuff that the tests detected to be broken. And probably
some more stuff that I felt like changing.

Changed the IntVar comparison operator semantics. Before, they would
return False for 'maybe'. Now, they return a Maybe object (which will
throw if anyone tries to convert it to bool). In the future, they will
return the result of a comparison constraint. BTW, this breaks the
existing constraints.

Commits like this are okay when you're in a rapid prototyping stage. ;)
Split domains!

Implemented as a list of min/max ints.

And I even got all the test cases to pass at the same time. :)
Add non-zero-non-five value to comparison tests