Regression introduced by the AttributeCore refactor combined with Node's use of _stateProxy and Node's custom setters.

a) The Attribute call to `var prevVal = this._getStateVal(attr);` moved from before the setter is called, to after it, as a runtime optimization from the re-factor; Don't need to get prevVal if we
failed validation for example.

b) Node leverages Attributes _stateProxy support, to store state somewhere other than _state (in this case to map to the dom node).

c) Node's setter for "value" sets the value on the _stateProxy [ build/node-attrs/node-attrs.js ]

As a result, for the `value` attribute, `(newVal === prevVal)` was always true, resulting in the event not firing, since `_getStateVal("value")`, would get the currently stored value from
`_stateProxy["value"]`, which had already been updated.

`set("title", "foo")` for example, works fine.