Relax polymorphism checks in static methods

[kriskowal]

These changes should improve the performance of polymorphic checks and
equality comparison in general. A method is no longer required to be on
the prototype, which was an unrealistic expectation of JavaScript in the
wild, but retains the ability to deeply compare object literals. The
code for comparing object literals will be exercised less frequently due
to additional checks to bail out early.

I could not bear to completely remove support for comparing object literals because equals should be useful down the line for a unit testing or assertion library and deep comparison of object literals is an expected behavior of equals as opposed to be or is.

[aadsm]

How about the array, could it be worthwhile to just rely on contentEquals and default to Object.is?

[kriskowal]

Consider:

expect(foo).equals([{index: 10}, {index: 20}, {index: 30}]);
expect(foo).equals([["a", 10], ["b", 20], ["c", 30]]);

I do think we have to retain equals as the default behavior. We can override contentEquals and contentCompare for specific arrays and equals and sorted will respect the change.

[aadsm]

I guess I'm happy with that, but I was expecting the other way around. I would assume that in that case, where you want a custom comparison (other than ===), you would define the contentEquals; but by default we'd have === comparison.