Added an improved blending algorithm for the new anti-aliasing routines after it occurred to me that it probably would not work for lighter coloured background.
Added an improved blending algorithm for the new anti-aliasing routines after it occurred to me that it probably would not work for lighter coloured background.

svn path=/trunk/; revision=7326

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