give us a parenStack which can grow to fit any input

Change-Id: Ic464184fe367da33bf8c4790b82656b140e3cbd0
(cherry picked from commit cced2f6b866877c39afe86f4af18622cb4022bef)
Reviewed-on: https://gerrit.libreoffice.org/13218
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Eike Rathke <erack@redhat.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>