TestCase.addTypeEqualityFunc

Add a type specific assertEqual style function to compare a type.

This method is for use by TestCase subclasses that need to register
their own type equality functions to provide nicer error messages.

Args:
    typeobj: The data type to call this function on when both values
            are of the same type in assertEqual().
    function: The callable taking two arguments and an optional
            msg= argument that raises self.failureException with a
            useful error message when the two arguments are not equal.