simpler Pair case.
	modified:   broom/ea.go
removed isString
	modified:   broom/builtin.go
	modified:   broom/object.go
	modified:   broom/object_test.go
removal of isNull
	modified:   broom/builtin.go
	modified:   broom/object.go
	modified:   broom/object_test.go
	modified:   broom/pair.go
	modified:   broom/pair_test.go