Revert to disabling the generate_plplot_h.inc target by default since it demands extra ocaml dependencies which most users probably won't have installed.  This time put a comment in ocaml.cmake to explain this.
Revert to disabling the generate_plplot_h.inc target by default since
it demands extra ocaml dependencies which most users probably won't
have installed.  This time put a comment in ocaml.cmake to explain this.

svn path=/trunk/; revision=11497

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