test: resurrect q_to_tab

New test may want to use this helper; keep it for them that do not
need to protect literal SP.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'jc/apply-ws-fix-tab-in-indent' into next

* jc/apply-ws-fix-tab-in-indent:
  test: resurrect q_to_tab