When using chained select, dependent doesn't clear value when the field it depends on clears

[jacklinke]

If using chained selects with filter_by,

1. Select a value in the filtering select field
2. Select a value in the filtered (dependent) select field
3. Change the filtering select field to a new value

The filtered select should be cleared out, because its existing value depended on the previous value of the filtering select, and may not actually be valid any longer.