Introduced -xor command line flag for testing the XOR mode; no longer the default.  Cleaned up the XOR demo code considerably.
Introduced -xor command line flag for testing the XOR mode; no longer
the default.  Cleaned up the XOR demo code considerably.

svn path=/trunk/; revision=2678

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