Attempting to load incorrect file in ctools_plugin_api_include()

Ctools_plugin_api_include() will require_once a file that is in $module_path/$file, if it exists. If not, it will check if DRUPAL_ROOT/$file exists, however will mistakenly load $module_path/$file (non-existent file) -- resulting in a fatal error.

This patch will include the intended file.

Now, I don't necessarily think it's a good idea to put your plugins in the Drupal root in the first place, but it looks like that was an intended feature of this function -- despite faulty ;)