Merge branch 'da/difftool'

Code clean-up in "git difftool".

* da/difftool:
  difftool: add a missing space to the run_dir_diff() comments
  difftool: remove an unnecessary call to strbuf_release()
  difftool: refactor dir-diff to write files using helper functions
  difftool: create a tmpdir path without repeated slashes

diff --cc builtin/difftool.c
Simple merge