gnuplot point size fix

[NoNick]

When gnuplot is used and poistSize is set, scalaplot produces no output image, only scatter.gpl.
Manual gnuplot execution is terminated with the following error (as I understood, gnuplot expects "pointsize" in lowercase):

$ gnuplot scatter.gpl

set pointSize 5.000000
    ^
"scatter.gpl", line 2: unrecognized option - see 'help set'.

Also pointsize parameter is ignored with style = XYPlotStyle.Dots, perhaps, warning should be raised when both these settings are set.

[NoNick]

Duplicate #11