Add examples 17 and 31 to the list of examples that is displayed.  Annotations of those examples still to be done.
Add examples 17 and 31 to the list of examples that is displayed.  Annotations
of those examples still to be done.

svn path=/trunk/; revision=9362

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