Changes access on plstream::set_stream() to make life easier for the wxwidgets driver.
Changes access on plstream::set_stream() to make life easier for the
wxwidgets driver.

svn path=/trunk/; revision=6380

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