Improve warnings when drawing mode setting/getting not supported by a device. 
Improve warnings when drawing mode setting/getting not supported by a
device. 

svn path=/trunk/; revision=12960

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