Add call to plseed in with the same initial seed used in the library.  This ensures that example 21 produces the same results as the C version  even though plseed has already been used in example 17.
Add call to plseed in with the same initial seed used in the library. 
This ensures that example 21 produces the same results as the C version 
even though plseed has already been used in example 17.


svn path=/trunk/; revision=9277

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