revert: add an XXX about rename tracking

We check for rename information in the dirstate. This is probably not enough to
preserve this behavior when using an explicit target rev.

I just spotted this while working on this code, but this is outside the scope
of my series so I'm just adding a comment to highlight this suspicious
situation.

mercurial/cmdutil.py

@@ -2450,6 +2450,7 b' def revert(ui, repo, ctx, parents, *pats'
         cwd = repo.getcwd()
         for f in dsadded:
             src = repo.dirstate.copied(f)
+            # XXX should we check for rename down to target node?
             if src and src not in names and repo.dirstate[src] == 'r':
                 dsremoved.add(src)
                 names[src] = (repo.pathto(src, cwd), True)