Respond to updates to a node.
This is a node-type-specific hook, which is invoked only for the node type being affected. See @link node_api_hooks Node API hooks @endlink for more information.
Use hook_node_update() to respond to node update of all node types.
This hook is invoked from node_save() after the node is updated in the node table in the database, before field_attach_update() is called, and before hook_node_update() is invoked.