Add alpha values for wxDC since a few derivatives of this do actually support transparency.
Add alpha values for wxDC since a few derivatives of this do actually support transparency.


svn path=/trunk/; revision=12273

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