Merge pull request #327 from bocoup/object-assign-extensions

test/built-ins/Object/assign/OnlyOneArgument.js

test/built-ins/Object/assign/assign-length.js

test/built-ins/Object/assign/invoked-as-ctor.js

test/built-ins/Object/assign/name.js

test/built-ins/Object/assign/source-get-attr-error.js

test/built-ins/Object/assign/source-non-enum.js

test/built-ins/Object/assign/source-own-prop-desc-missing.js

test/built-ins/Object/assign/source-own-prop-error.js

test/built-ins/Object/assign/source-own-prop-keys-error.js

test/built-ins/Object/assign/target-set-not-writable.js

test/built-ins/Object/assign/target-set-user-error.js