Wrong behavior of the gnuplot backend

[Luca Manzari]

Hi all,

Plotting multiple axes on the same figure works with the fltk and qt 
backends, does not with the gnuplot backend. Change the backend name 
(gnuplot/qt/fltk) as needed to experiment.

%%%%%%%%%%%%%%%%%

graphics_toolkit("gnuplot")

figure

line(1:10, 1:10)

ax1 = gca;
ax1_pos = get(ax1,'position');

ax2 = axes('position', ax1_pos, ...
           'xaxislocation', 'top', ...
           'yaxislocation', 'right', ...
           'Color','none');

line(1:10, 10:-1:1, 'Color','r')

%%%%%%%%%%%%%%%%%

Tested on a Windows machine, Octave 4.2.0. On a Debian 8 machine with 
Octave 4.2.0 I can only test the gnuplot backend, and it behaves the 
wrong way like on the Windows machine. Any ideas?

--
Luca