title: Symfony 2 cache clearing issue
body: <p>My Symfony 2 website has recently been giving me problems when I try to clear the cache.
  I type the following command in the terminal:</p>
  
  <pre><code>php app/console cache:clear --env=dev
  </code></pre>
  
  <p>And get the following error:</p>
  
  <pre><code>[ErrorException]                                                                                                                                                                                                                                   
   Warning: rename(/var/www/corpsite/corpsite/app/cache/dev,/var/www/corpsite/corpsite/app/cache/dev_old): Directory not empty in /var/www/corpsite/corpsite/vendor/symfony/src/Symfony/Bundle/FrameworkBundle/Command/CacheClearCommand.php line 74  
  </code></pre>
  
  <p>So I change the permissions on that file to 777, and re-run the clear cache command, which gives me this error:</p>
  
  <pre><code>  [ErrorException]                                                                                                                                                                                                                         
    Warning: unlink(/var/www/corpsite/corpsite/app/cache/dev_old/twig/6b/e9/4491e41b895786689b86f32f446f.php): Permission denied in /var/www/corpsite/corpsite/vendor/symfony/src/Symfony/Component/HttpKernel/Util/Filesystem.php line 100  
  </code></pre>
  
  <p>I can get round the problem by deleting the 'dev_old' folder, but I want to solve the problem that is causing the issue.</p>
  
  <p>P.S - I am aware the site is running in dev mode. The site has been live for 10 months and this has never been an issue before.</p>
  
  <p>Any help is appreciated!</p>