Get rid of -DHAVE_PTHREAD=ON warning for CMake-2.6.x.
Get rid of -DHAVE_PTHREAD=ON warning for CMake-2.6.x.

svn path=/trunk/; revision=8531

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