title: Ignore migration by Django verison
body: <p>I am migrating a project from Django 1.7 to 1.8 and I need to run an extra migration script to support a user model. </p>
  
  <p>By the way, I need to save the compatibility with the 1.7 version which this migration makes it wrong.</p>
  
  <p>As the migration scripts are auto-generated is there still any way to add some conditions to avoid running some specific migrations by version of Django?</p>