Created to keep all the junk common to the C demos.  Helps to keep me from cluttering up plplot.h.
Created to keep all the junk common to the C demos.  Helps to keep me
from cluttering up plplot.h.

svn path=/trunk/; revision=1542

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot