Further corrections to parenting of axes (bug #39813) * scripts/plot/util/newplot.m: Accept multiple graphic handles to save. Also save handles when axis nextplot property is "replacechildren". Correct failing %!test. * scripts/plot/util/__plt_get_axis_arg__.m: Return axis as first value, "parent" handle as second value. * scripts/plot/draw/surface.m: Get axis from __plt_get_axis_arg__ and ignore any other returned handles.