[PATCH] x11 terminal is now less zealous about replotting

[Dima K. <gn...@di...>]

I'm attaching a patch to the x11 terminal to reduce the number of
unneeded replot actions that happen with some window managers.

Some window managers (notion for instance) produce several
ConfigureNotify events when a window is created. Some of these were
mis-interpreted by gnuplot as a window manager refusing gnuplot's
suggested resize, which resulted in extra, unneeded replot actions. This
patch waits 0.1s for extra ConfigureNotify events before deciding that a
resize was rejected. If a new ConfigureNotify is seen, we save a replot
at the cost of 0.1s. If not, we proceed as before.