title: makemigrations does not work after deleting migrations
body: <p>I mistakenly deleted all the <strong>.py</strong> file under path <strong>projectName/appName/migrations</strong>, it include like:</p>
  <blockquote>
  <p>0001_initial.py</p>
  <p>0011_auto_20150918_0723.py</p>
  <p>0002_auto_20150819_1301.py</p>
  <p>...</p>
  </blockquote>
  <p>Now, even I updated the <strong>Model</strong> file, and run the command <code>python manage.py makemigrations</code>, it always prompt with <strong>No changes detected</strong>.</p>
  <p>How can I recover everything?</p>