Include plConfig.h now, to pick up definition of PL_DOUBLE that was set at configuration time.
Include plConfig.h now, to pick up definition of PL_DOUBLE that was
set at configuration time.

Fix PLPLOT_VERSION to reflect that we are now on the 5.1 development
branch.

svn path=/trunk/; revision=2111

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