Merge branch 'jc/rerere-train' into maint

A contrib script "rerere-train" did not work out of the box unless user
futzed with her $PATH.

* jc/rerere-train:
  contrib/rerere-train: use installed git-sh-setup

contrib/rerere-train.sh

@@ -7,7 +7,7 @@ USAGE="$me rev-list-args"
 
 SUBDIRECTORY_OK=Yes
 OPTIONS_SPEC=
-. git-sh-setup
+. $(git --exec-path)/git-sh-setup
 require_work_tree
 cd_to_toplevel