title: Django - FilePathField returns wrong paths
body: <p>I'm trying to allow admin to choose from flags when they creates neww <code>Language</code> object. </p>
  
  <p>There is a folder <code>mainapp/static/img/flags/550px/</code> with <code>*.png</code> images of flags. </p>
  
  <pre><code>class Language(models.Model):
      shortcut = models.CharField(max_length=40,
                                  help_text=_('Shortcut of the language'),
                                  unique=True)
  
      name = models.CharField(max_length=40,
                              help_text=_('Name of the language'),
                              unique=True, verbose_name=_("Language"))
  
      flag = models.FilePathField(path='mainapp/static/img/flags/550px'),default='/static/img/icons/check-icon.png')
      #flag = models.FilePathField(path='{}\mainapp/static/img/flags/550px'.format(settings.BASE_DIR),default='/static/img/icons/check-icon.png')
  </code></pre>
  
  <p>The problem is that Django doesn't resolve those paths in html. There are paths like this: <code>mainapp/static/img/flags/550px\es.png</code> which is a problem because Django starts in <code>/static/</code>, not <code>/mainapp/</code>.</p>
  
  <p>On the other hand, when I put <code>static/img/flags/550px</code>, it does not let me choose from the folder.</p>
  
  <p>So the main problem is that when admin choose from flags, it saves path with <code>mainapp/static..</code> at the beginning. I want to save only <code>static/..</code></p>
  
  <p>Do you know what should I do?</p>