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/axes.m
+++ b/scripts/plot/axes.m
@@ -57,8 +57,7 @@
   else
     ## ARG is axes handle.
     htmp = varargin{1};
-    if (isscalar (htmp) && ishandle (htmp)
-        && strcmp (get (htmp, "type"), "axes"))
+    if (isscalar (htmp) && isaxes (htmp))
       if (__is_handle_visible__ (htmp))
         parent = ancestor (htmp, "figure");
         set (0, "currentfigure", parent);