Merge pull request #320 from bocoup/WeakSet

test/built-ins/WeakSet/add-not-callable-throws.js

test/built-ins/WeakSet/constructor.js

test/built-ins/WeakSet/empty-iterable.js

test/built-ins/WeakSet/get-add-method-failure.js

test/built-ins/WeakSet/iterable-failure.js

test/built-ins/WeakSet/iterable.js

test/built-ins/WeakSet/iterator-close-after-add-failure.js

test/built-ins/WeakSet/iterator-next-failure.js

test/built-ins/WeakSet/iterator-value-failure.js

test/built-ins/WeakSet/length.js

test/built-ins/WeakSet/name.js

test/built-ins/WeakSet/no-iterable.js

...ins/WeakSet/properties-of-the-weakset-prototype-object.js

test/built-ins/WeakSet/prototype-of-weakset.js

...akSet/prototype/Symbol.toStringTag/property-descriptor.js

test/built-ins/WeakSet/prototype/add/add.js

test/built-ins/WeakSet/prototype/add/adds-element.js

...type/add/does-not-have-weaksetdata-internal-slot-array.js

...totype/add/does-not-have-weaksetdata-internal-slot-map.js

...ype/add/does-not-have-weaksetdata-internal-slot-object.js