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/plotmatrix.m
+++ b/scripts/plot/plotmatrix.m
@@ -109,8 +109,7 @@
 function plotmatrixdelete (h, d, ax)
   for i = 1 : numel (ax)
     hc = ax(i);
-    if (ishandle (hc) && strcmp (get (hc, "type"), "axes")
-        && strcmpi (get (hc, "beingdeleted"), "off"))
+    if (isaxes (hc) && strcmpi (get (hc, "beingdeleted"), "off"))
       parent = get (hc, "parent");
       ## If the parent is invalid or being deleted, then do nothing
       if (ishandle (parent) && strcmpi (get (parent, "beingdeleted"), "off"))