Add %f token for files directory in "Define CSS" setting

My goal was the next: I'm using the module less. This creates a new path in file system, and makes own css files. I thought, why can't define only path, if use settings "Define css" in Editor CSS field, and could load all css file within this path.

This patch makes a new placeholder %f to filesystem. If not .css file set, try to load .css files in directory. You can define '%f/css', if you want use the aggregated css files, or using modules less the correct path is: "%f/%t/[css_path_in_your_theme]". If css file couldn't loaded, set an error message.
I try to make this all of editors, where this settings enabled, but couldn't test it now. When I checked coder, it tells some minor bug, these are corrected too.

This is the base code for tinymce:

  if (isset($config['css_setting'])) {
    if ($config['css_setting'] == 'theme') {
      $settings['content_css'] = implode(',', wysiwyg_get_css());
    }
    elseif ($config['css_setting'] == 'self' && isset($config['css_path'])) {
      $csspath = strtr($config['css_path'], array('%b' => base_path(), '%t' => path_to_theme(), '%f' => file_directory_path()));
      if (preg_match('/.*\.css$/', $csspath)) {
        $settings['content_css'] = $csspath;
      }
      else {
        global $base_url;
        $cssfiles = file_scan_directory($csspath, '.*\.css$');
        if ($cssfiles) {
          foreach ($cssfiles as $key) {
            $filesarray[] = $base_url . '/' . $key->filename;
          }
        $settings['content_css'] = implode(',', $filesarray);
        }
        else {
          if (user_access('administer filters')) {
            drupal_set_message(t("The wysiwyg css path is not configured properly. Check the !settings_url settings page!", array('!settings_url' => l(t('Wysiwyg profiles'), 'admin/settings/wysiwyg'))), 'error');
          }
        }
      }
    }
  }