title: How to filter a dropdownlist in Django's admin when a selection is made on another dropdownlist
body: <p>I have two dropdownlists in a Django admin site. For example, I have SelectCountry and SelectRegion. Region has a foreignkey relationship to Country. How do I ensure that when a Country is selected, the Regions are filtered based on that Country?</p>
  
  <p>N.B: I am using django-grappelli for my admin backend as well.</p>
  
  <p>Any ideas will be appreciated. Thanks.</p>