Client-side tracking of renames

Subversion's client should track renames/moves (which are modeled as
copy+delete) as renames/moves, disallowing independent actions on the copy or
delete halves of the operation, and binding the two together with metadata
suitable for transmission across the RA layer.

A revert of half of a rename should be disallowed, or should revert both halves.
A commit of half of a rename should be disallowed, or should commit both halves.
etc.