Convert node type on upgrade

After running event_upgrade.php, none of my existing events showed up in the calendar view. Since event nodes are now based on flexinode, the event type in the node table needs to be in the 'flexinode-n' form.

At some appropriate point in event_upgrade.php, the query "UPDATE {node} set type='flexinode-$ctype_id' where type='event'" should be executed.