#770 gnuplot is not working

[Jason Fuller]

Gnuplot doesn't seem to work anymore (in v3.0 and newer). Adding this object (or any combo of output/file):

object recorder{

parent ourHouse;
property air_temperature;
interval 3600;
limit 240;
output JPG;
file plot:player_adb.jpg;

}

to a model with a house produces a blank PLOT file.

While finicky, it seems to work okay in v2.3.