allow zooming for logscale plots * graphics.cc (axes::properties::zoom_about_point): Allow zooming for logscale axes. * graphics.h.in (class neg_log_scaler): New class. (log_scalar::do_neg_scale): Delete (log_scalar::scale): Don't attempt to handle negative data. (axes::properties::get_scale): New function. (axes::properties::update_xscale, axes::properties::update_yscale, axes::properties::update_zscale): Use it. (axes::properties::update_xlim): Call update_xscale. (axes::properties::update_ylim): Call update_yscale. (axes::properties::update_zlim): Call update_zscale.

--- a/src/graphics.cc
+++ b/src/graphics.cc
@@ -6632,11 +6632,8 @@
   double max_neg_y = -octave_Inf;
   get_children_limits (miny, maxy, min_pos_y, max_neg_y, kids, 'y');
 
-  if (! xscale_is ("log"))
-    xlims = do_zoom (x, factor, xlims, xscale_is ("log"));
-
-  if (! yscale_is ("log"))
-    ylims = do_zoom (y, factor, ylims, yscale_is ("log"));
+  xlims = do_zoom (x, factor, xlims, xscale_is ("log"));
+  ylims = do_zoom (y, factor, ylims, yscale_is ("log"));
 
   zoom (xlims, ylims, push_to_zoom_stack);
 }