Use iuc/package_gnuplot_4_6 dependency now on Test Tool Shed
Input test case FASTA files from MUMMER documentation

http://mummer.sourceforge.net/examples/data/B_anthracis_contigs.fasta
http://mummer.sourceforge.net/examples/data/B_anthracis_Mslice.fasta

Used in the nucmer example.
mummerplot test output (used gnuplot 4.2 patchlevel 6)
Include mummerplot test case
Try to test mummerplot on TravisCI