I have discovered this annoying issue when using rgplot from a ruby script with warnings enabled. The problem is that
the gnuplot data is printed to stdout if warnings are turned on - and this breaks my pipeline (piping data on a bash
command line). I think it would be fair that this data should be printed to stderr instead.

This is the offending line:

./lib/gnuplot.rb:      puts "writing this to gnuplot:\n" + to_gplot + "\n" if $VERBOSE

I suggest

$stderr.puts "writing this to gnuplot:\n" + to_gplot + "\n" if $VERBOSE

Cheers and thanks for an awesome gem!