Consider allowing select.value & option.value bound value to be object-valued

The idea here is that it's often useful to have a selector whose value is a domain object.

IOW

``` JavaScript
model = {
  users: [{ name: 'Bob', id: 1}, { name: 'Sally', id: 2}];
  selected: undefined
}
```

``` HTML
<select value={{ selected }}>
  <option template repeat="{{ user in users }}" value="{{ user }}">{{ user.name }}</option>
</select>
```
