gnuplot changes affects octave

[Dmitri A. Sergatskov]

Recently gnuplot (version 4.1) changed the way it handles NaN and
their meaning. That affects gplot.m and probably some other octave
scripts.

E.g. consider the following data file (say "test1.dat")

# -- begin --
0 1
1 0
NaN NaN
1 2
2 1
# -- end

In gnuplot 4.0
plot "test1.dat" with line
will produce two line segments; NaN are handled automatically.

In gnuplot 4.1 one needs to do first
set datafile missing "NaN"
(note that will *not* handle "nan" only "NaN)
but than it will connect the segments between (1 0) and (1 2).

If one replaces line that has NaNs with an empty line, the connecting
segment will not be there.

Sincerely,

Dmitri.
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