title: "Fixed default value provided" after upgrading to Django 1.8
body: <p>Django 1.8 now has some problem detection for models, which is nice.  However, for one warning that it is giving me, I understand the problem, but I don't understand how the hint that it is giving me is any better.</p>
  
  <p>This is my (bad) model field:</p>
  
  <pre><code>my_date = DateField(default=datetime.now())
  </code></pre>
  
  <p>and it's easy to see why that's bad.  But this is the hint it's giving me:</p>
  
  <blockquote>
    <p>MyMoel.my_date: (fields.W161) Fixed default value provided.<br>
        &nbsp;&nbsp;&nbsp;&nbsp;HINT: It seems you set a fixed date / time / datetime value as default for this field. This may not be what you want. If you want to have the current date as default, use `django.utils.timezone.now`</p>
  </blockquote>
  
  <p>So, it says to use <code>timezone.now</code>, but how is that any better than <code>datetime.now</code>?  They're <em>both</em> "fixed default" values... <code>timezone.now</code> just <em>returns</em> a datetime instance, which is a fixed value...</p>
  
  <p>I suspect that it actually wants me to insert some sort of flag that says "use <code>timezone.now</code> <em>later</em>".  But that's not what the hint says... so what is that flag?</p>