Configurable option for locking outline pages

Issue Summary

Ref.:

"For example, on node/%/outline we need to check for book.module's "administer outline" permission."
http://drupal.org/node/422870#comment-1712914

Should Checkout lock on node/%/outline ?

If I recall correctly, using outline does not alter the time stamp or content of a node, so does that mean that two people could perform those two kinds of updates on the same node at the same time? (outline and edit)

If so, then I assume that the reason for locking on node/%/outline could be to prevent more than one user to use the node/%/outline at the same time, not related to avoid conflicts with the editing of the node.

If the above makes sense, then I wonder:

- is there a way to only lock the node on node/%/outline, and still not lock the edit possibility? Maybe not, as this is record-locking, unless the fields affected by an outline operation outline are not affecting that same node record in the database. I have not checked that.

Main point:
How often would we run into a situation where there is a real problem with two (or more) using the outline function on the same node simultaneously? Would it be more annoying than relieving to have locking on that function?

On busy sites, I can see the need for this, but most/smaller sites are not so terribly busy, so I wonder if the default should be optimistic locking for the outline, with a configurable option so that extra busy sites could choose to lock on outline when desired.