plot buffer also handles "Clear Background" escape function. This should have no impact on drivers which don't support this escape function, since in that case a filled polygon with the background color will be drawn in the first place and this escape function never recorded by the buffer.
plot buffer also handles "Clear Background" escape function. This should have no impact on drivers which don't support this escape function, since in that case a filled polygon with the background color will be drawn in the first place and this escape function never recorded by the buffer.

svn path=/trunk/; revision=9073

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