Merge branch 'ar/maint-mksnpath' into ar/mksnpath

* ar/maint-mksnpath:
Use git_pathdup instead of xstrdup(git_path(...))
git_pathdup: returns xstrdup-ed copy of the formatted path
Fix potentially dangerous use of git_path in ref.c
Add git_snpath: a .git path formatting routine with output buffer

Conflicts:
builtin-revert.c
refs.c
rerere.c