"git check-attr" when (trying to) work on a repository with a
working tree did not work well when the working tree was specified
via --work-tree (and obviously with --git-dir).

The command also works in a bare repository but it reads from the
(possibly stale, irrelevant and/or nonexistent) index, which may
need to be fixed to read from HEAD, but that is a completely
separate issue.  As a related tangent to this separate issue, we
may want to also fix "check-ignore", which refuses to work in a
bare repository, to also operate in a bare one.

* jc/check-attr-honor-working-tree:
  check-attr: move to the top of working tree when in non-bare repository
  t0003: do not chdir the whole test process