crash on node deletion

The application crashes when we try to delete a node in production using Sphinx because "search.pid" is not readable.

We need to fix rake/capistrano tasks to ensure that searchd.pid is world readable.

If you need to delete node without version:

mysql> select nodes.id, name from nodes left join versions on versions.node_id = nodes.id where versions.id is null;
mysql> delete nodes where id = xxxxx;

Another fix: transactions !