Fixed png graphics device call

Replaced dev.copy with explicit call to png graphics device
Corrected plot

The legend is no longer squashed.  The legend’s line colors are
corrected.
Changed call to graphics device

Removed dev.copy().  Made call to png graphics device.  This apparently
changed plot1.png.
Changed call to png graphics device

Removed dev.copy() .  Made call to png graphics device explicit.
Added comment