Proposing a change to linestyle FIXME

[Jarno Rajahalme]

I was unable to print plots with solid lines. A simple plot with two line 
objects, each set to linestyle "-", would print with one line solid, other 
dashed. Even the "whiskers" in the errorbars were printing as various dashed 
lines, when including multiple errorbars on the same plot.!

Using hours to dig up the cause I found this in __go_draw_axes__.m

    ## FIXME -- linetype is currently broken, since it disables the
    ## gnuplot default dashed and solid linestyles with the only
    ## benefit of being able to specify '--' and get a single sized
    ## dashed line of identical dash pattern for all called this way.
    ## All dash patterns are a subset of "with lines" and none of the
    ## lt specifications will correctly propagate into the x11 terminal
    ## or the print command.   Therefore, it is currently disabled in
    ## order to allow print (..., "-dashed") etc. to work correctly.

    ##    if (! isempty (lt))
    ##      fprintf (plot_stream, " linetype %s", lt);
    ##    endif

Changing the commented code to the following allows linetypes set to "-" to 
always print as solid lines:

    ## Jarno Rajahalme 2.11.2010
    ## Allow lt 1 to go through to force solid lines, use "--" to use
    ## the various dashed backend linestyles
    if (! isempty (lt))
      if (lt == "1")
        fprintf (plot_stream, " linetype %s", lt);
      endif
    endif

This is not any prettier than the disabling the linetype setting, but I think 
this works better. Octave's errorbar code uses linetype "-" for the error 
"whiskers", and with this change they actually print like they should, even 
when plotting multiple errorbars on the same plot.

So, with this change, linestyle "-" always produces solid lines, whereas 
linestyle "--" produces the various different dashed lines produced by gnuplot 
(by backend) to the EPS printout.

Regards,

  Jarno