Update ndiff cmake support to link in gmp if available and to install the binary and man page.
Update ndiff cmake support to link in gmp if available and to install the binary and man page.


svn path=/trunk/; revision=12251

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