Assimilate undo-tree release/0.6.6-4-g597575e3 from emacsg

.gitmodules

@@ -40,6 +40,10 @@
 [submodule "packed"]
 	path = lib/packed
 	url = git@github.com:tarsius/packed.git
+[submodule "undo-tree"]
+	path = lib/undo-tree
+	url = http://www.dr-qubit.org/git/undo-tree.git
+	remote = emacsg git@github.com:emacscollective/undo-tree.git
 [submodule "use-package"]
 	path = lib/use-package
 	url = git@github.com:jwiegley/use-package.git

init.el

@@ -154,6 +154,11 @@
   (add-to-list 'tramp-default-proxies-alist
                (list (regexp-quote (system-name)) nil nil)))
 
+(use-package undo-tree
+  :config
+  (global-undo-tree-mode)
+  (setq undo-tree-mode-lighter ""))
+
 (progn ;     startup
   (message "Loading %s...done (%.3fs)" user-init-file
            (float-time (time-subtract (current-time)

lib/undo-tree

@@ -0,0 +1 @@
+Subproject commit 597575e35bc26fbe66dad6d27508aa936d61bdde