Merged from upstream with StefanM's changes

diff --cc packages/ztree/README.md
Simple merge

diff --cc packages/ztree/ztree-diff-model.el
Simple merge

diff --cc packages/ztree/ztree-diff.el
Simple merge

diff --cc packages/ztree/ztree-dir.el
Simple merge

diff --cc packages/ztree/ztree-util.el
Simple merge

diff --cc packages/ztree/ztree-view.el
Simple merge

diff --cc packages/ztree/ztree.el
Simple merge