Added code to start plserver with sigprocmask set so that a ^C doesn't kill it (enabled if pls->server_nokill is set).  Contributed by Ian Searle.
Added code to start plserver with sigprocmask set so that a ^C doesn't
kill it (enabled if pls->server_nokill is set).  Contributed by Ian
Searle.

svn path=/trunk/; revision=1156

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