title: Using normalizer with ReduxForm results in form always being dirty
body: <p>I'm using a normalizer to convert ISO 8601 date/time values (<em>e.g</em> <code>2016-05-24T20:38:34+00:00</code>) coming from a rest api to simply a date (<em>e.g</em> <code>2016-05-24</code>). My normalizer looks like this:</p>
  
  <pre><code>export const dateNormalizer = function(value){
      if(value)
          return moment(value).format("YYYY-MM-DD");
      };
  </code></pre>
  
  <p>I also use a normalizer for currency conversion (<em>e.g.</em> making sure it's only numbers, etc).</p>
  
  <p>The problem I'm facing is that this is causing the form to <em>always</em> be dirty. In other words, as soon as the initial state is loaded (via <code>initialValues</code> in <code>mapStateToProps</code>) <code>this.props.dirty</code> always returns true. Even dispatching a <code>reset</code> doesn't result in <code>dirty=false</code>. </p>
  
  <p>Is there a way to overcome this? The issue I'm having is that I want to be able to display a warning to the user that they're about to abandon their changes without having to implement my own <code>onChange</code> override for each input field, and right now they're <em>always</em> warned about abandoned changes.</p>