Merge branch 'js/fsck-name-object'

Merge branch 'js/fsck-name-object'

When "git fsck" reports a broken link (e.g. a tree object contains
a blob that does not exist), both containing object and the object
that is referred to were reported with their 40-hex object names.
The command learned the "--name-objects" option to show the path to
the containing object from existing refs (e.g. "HEAD~24^2:file.txt").

* js/fsck-name-object:
  fsck: optionally show more helpful info for broken links
  fsck: give the error function a chance to see the fsck_options
  fsck_walk(): optionally name objects on the go
  fsck: refactor how to describe objects