need to gracefully handle old gnuplot versions
We should check the gnuplot version either at configure time or at run time (or both) via gnuplot --version to make sure that it is new enough to support the options used by darshan-job-summary.pl
We should check the gnuplot version either at configure time or at run time (or both) via gnuplot --version to make sure that it is new enough to support the options used by darshan-job-summary.pl