Avoid trailing slashes when passing file paths to file_check_directory()

Hi,

the FeedsHTTPBatch files are stored in /files/ instead of /files/feeds/, due to a small "bug" in FeedsBatch.inc:

      $dir = file_directory_path() .'/feeds/';

      if (!file_check_directory($dir, TRUE)) {
        throw new Exception(t('Feeds directory either cannot be created or is not writable.'));
      }

      $dest = file_destination($dir . get_class($this) .'_'. drupal_get_token($this->url) .'_'. time(), FILE_EXISTS_RENAME);

The problem is that file_check_directory trims all starting and trailing slashes "/".

The solution looks like this (see my comments):

      // morningtime: removed trailing /
      $dir = file_directory_path() .'/feeds';

      if (!file_check_directory($dir, TRUE)) {
        throw new Exception(t('Feeds directory either cannot be created or is not writable.'));
      }

      // morningtime: re-added trailing / 
      $dest = file_destination($dir . '/' . get_class($this) .'_'. drupal_get_token($this->url) .'_'. time(), FILE_EXISTS_RENAME); 

Now files are stored in /files/feeds/ again.

Patch attached for HEAD.