Merge branch 'jk/repo-info-path-keys' into jch

Merge branch 'jk/repo-info-path-keys' into jch

The "git repo info" command has been taught new keys to output both
absolute and relative paths for "gitdir" and "commondir", supported by
a new path-formatting helper extracted from "git rev-parse".

* jk/repo-info-path-keys:
  repo: add path.gitdir with absolute and relative suffix formatting
  repo: add path.commondir with absolute and relative suffix formatting
  path: extract format_path() and use in rev-parse