improving axes property behavior for the gnuplot backend

[Ben Abbott]

As implemented today, the gnuplot backend does not properly respect  
the "outerposition", "position" and "activepositionproperty"  
properties for the axes. For the gnuplot backend to do so a rather  
signficant change to __go_draw_axes__.m is needed.

I'm thinking about taking that on. Before begining I wanted solicit  
comments/concernts/objections.

In order to ensure that the "position" and "outerpostion" are rendered  
properly and are consistent across different terminals, I suspect it  
will also be necessary to replace the gnuplot x/y/zlabel commands with

set label {<tag>} {"<label text>"}
    {at {<system>} <x>, {<system>} <y> {,{<system>} <z>}}
    {left | center | right}
    {norotate | rotate {by <degrees>}}
    {font "<name>{,<size>}"}
    {noenhanced}
    {front | back}
    {textcolor <colorspec>}
    {point <pointstyle> | nopoint}
    {offset <offset>}

Again, before I begin does anyone have any comments/concerns/objections?

Ben

p.s. ticklabels might also be explicitly positioned by Octave, but  
that can wait.