Change various plot functions to take advantage of new isaxes() function. * scripts/geometry/voronoi.m, scripts/image/imagesc.m, scripts/plot/__plt_get_axis_arg__.m, scripts/plot/axes.m, scripts/plot/cla.m, scripts/plot/colorbar.m, scripts/plot/hold.m, scripts/plot/legend.m, scripts/plot/plotmatrix.m, scripts/plot/plotyy.m, scripts/plot/private/__errplot__.m, scripts/plot/private/__plt__.m, scripts/plot/view.m: Use new isaxes function to simplify code. * scripts/plot/shading.m: Use Octave convention for spacing of parentheses. * scripts/plot/zlabel.m: Correct %!test incorrectly calling plot3 with figure handle.

--- a/scripts/plot/shading.m
+++ b/scripts/plot/shading.m
@@ -64,7 +64,7 @@
     types = get (kids, "type");
     hlist = [hlist; kids(strcmp(types, "patch"))];
     hlist = [hlist; kids(strcmp(types, "surface"))];
-    parents = kids(strcmp(types, "axes"));
+    parents = kids(strcmp (types, "axes"));
     hglist = kids(strcmp (types, "hggroup"));
     for i = 1 : numel (hglist)
       props = get (hglist(i));