Upgrade to leverage Angular 1.3.X $validators and tweak model update behavior when view value is not valid

So while this directive works fine in Angular 1.3.X, I feel that it should take advantage of the new ```$validators``` pipeline available on the ```NgModelController```.

This PR:
- Upgrades Angular dependencies to ~1.3.4
- Updates min/max validation to use ```$validators```
- Changes the expected behavior, such that the model value is invalidated and set to ```undefined``` when the view value does not pass validation

A couple of thoughts: 
- Most controversial change in this PR is probably the change in behavior around model value updates on invalid view value changes
- Do people even want this and should there be a separate branch for 1.3.X version of the plugin?