title: Django & Postgresql & South: convert CharField to DecimalField
body: <p>I've changed a CharField to DecimalField and got this error from South:</p>
  
  <p>HINT:  Specify a USING expression to perform the conversion</p>
  
  <p>So I googled it and used this:</p>
  
  <blockquote>
  <pre><code>    db.execute(
          'ALTER TABLE "user_profile" '
          'ALTER COLUMN "proxy_score" DROP DEFAULT, '
          'ALTER COLUMN "proxy_score" DROP NOT NULL, '
          'ALTER COLUMN "proxy_score" TYPE NUMERIC USING to_number("proxy_score", "99.99")'
      )
  </code></pre>
    
    <p>this is the error I'm getting after running my migration code through south: django.db.utils.DatabaseError: column "99.99" does not exist </p>
  </blockquote>
  
  <p>but something is wrong with my to_number.</p>
  
  <p>What am i missing? </p>
  
  <p>I would like to support 4 digits decimal number for example: 12.35</p>
  
  <p>Thanks</p>