Node postsave hook

I have added this hook myself to my core for several custom modules.
It is especially useful when you need to act on a nodeid just after initial creation, such as applying changes to a node using the tokens module.

Without this, the nodeid will not exist until after the node has been created at which point you've lost the ability to hook it.

I currently use it in production for a much simpler way to deal with changing upload paths based on the node information. This never worked on initial node creation simply and smoothly until I added this hook.

I implemented this as a one line change to node.module:

  // Call the node specific callback (if any).

  node_invoke($node, $op);

  node_invoke_nodeapi($node, $op);

  node_invoke_nodeapi($node, 'postsave');



  // Update the node access table for this node.

  node_access_acquire_grants($node);

Alternate simple methods to achieve the same result are welcome.