Add a mouse interactive rubber-banding rectangle facility, in function "plrb".
Add a mouse interactive rubber-banding rectangle facility, in function "plrb".

svn path=/trunk/; revision=3946

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