title: PHP_CodeSniffer to check for file extensions in a folder
body: <p>I am using the CakePHP framework, and would like to have PHP_CodeSniffer warn against image files that developers might in a haste, paste into the <code>app/webroot/css</code> folder while copying in something, as opposed to moving them into an appropriate folder in <code>app/webroot/img</code>.</p>
  
  <p>Is this a bad idea? If not, how do I write a custom sniff to do this?</p>