nonlinear3.dem is very slow on aqua terminal

[Jun T. <tak...@kb...>]

With terminal aqua, nonlinear3.dem takes *very* long time.
It took about 8 minutes on my Mac.

This is a problem of Aquaterm.app (or its API); it is designed
for vector graphics (and works very well for vector graphics),
but can't handle bitmap graphics properly (slow, and uses
lots of memory).

Since most Mac users would think gnuplot has gone into an
infinite loop and try to kill gnuplot (or Aquaterm) before
the demo finishes, I think it would better to skip this
demo in all.dem, as in the attached patch.