ng-model-options debounce seems to still trigger "dirty model checking" cycle

[pjfsilva]

I was expecting that the debounce option of ngModelOptions can be used to improve the performance by avoiding triggering too many watches on my page.

On my use case for example, I have a table where I apply 1 filter per cell (yes, I know I can optimize that) and 1 form with some input fields. Without using debounce for every keypress on an input field all my filters are executed which is a big no-no.
From my tests it seems that the debounce works correctly by only updating the model "after the debounce". The problem is that I still see the filters being called on every keypress which is something I wasn't expecting.

Steps to reproduce:

1. Go to http://plnkr.co/edit/CHX2kA
2. Open developer tools to see console.log output
3. Type something on the input field: I was expecting that the filter used on the page was only executed when the debounce "finishes" and the model is updated but it is still called for every keypress.

Tested on angular v1.3.0-beta.19

[caitp]

Moving to same milestone as fix