Tweak to accommodate move of plbuf.c from ../drivers to this directory (src).
Tweak to accommodate move of plbuf.c from ../drivers to this directory (src).

svn path=/trunk/; revision=4315

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