Update on the branch surgery

[<es...@th...>]

I have successfully transplanted 4.2, but 4.0 has a problem.  Rebasing
it on /#include gp_time.h/ yields this diff at the tip:

--- a/demo/gnuplot.rot	1998-04-22 09:38:42.000000000 -0400
+++ b/demo/gnuplot.rot	2017-10-25 17:39:55.083147765 -0400
@@ -1,12 +1,5 @@
-# HBB: revised open-ended animation routine. Used to just turn
-# round and round by somewhat large steps. Now, it tumbles
-# back and forth smoothly.
-# If 'limit_iterations' is set to a nonzero value, it'll stop after that
-# many iterations (iteration_count=0 has to be set before this
-# script is called)
 zrot=(zrot+10)%360
 xrot=(xrot+17)%180
-set view (50.+30.*sin(xrot/180.*pi)),60.+45.*sin(zrot/180.*pi)
+set view xrot,zrot
 replot
-iteration_count=iteration_count+1
-if ((!limit_iterations) || (iteration_count<=limit_iterations)) reread
+reread
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>

"Rightful liberty is unobstructed action, according to our will, within limits
drawn around us by the equal rights of others."
	-- Thomas Jefferson