Clients need to be able to specify interest in a remote node, so that it isn't cleaned up during normal cleanup routines. Specifically, we need this for markup view's Undo feature when deleting, that keeps around a reference to a detached node in case of undo.

The debugger's threadGrip request does something similar (promote pause-scoped grips to thread-scoped ones). We should probably generalize the concept and harmonize the implementations at some point.

Hopefully this is the last of the tree-fiddling patches.

v2 depends on this small patch

Paul - I think dcamp gave us both reviews because either of us could review this, not because both of us should review it. So I think you can skip this.

Timing!