Merge branch 'maint'

* maint:
tutorial: gentler illustration of Alice/Bob workflow using gitk
pretty=format: respect date format options
make git-shell paranoid about closed stdin/stdout/stderr
Document gitk --argscmd flag.
Fix '--dirstat' with cross-directory renaming
for-each-ref: Allow a trailing slash in the patterns

diff --cc commit.h
Simple merge

diff --cc diff.c
Simple merge

diff --cc shell.c
Simple merge