Fix behavior of ReactDOMSelect

Closes #250.

Test Plan:
With multiple and not, verified: With defaultValue, the correct option is picked initially, user changes change the selection, and changes to defaultValue have no effect. With value, the correct option is picked initially, user changes do nothing, and changes to value change the selection.

Also ran the tests.
Merge pull request #251 from spicyj/select-value

Fix behavior of ReactDOMSelect with `defaultValue`