Unreleased fixes in master

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

Hi.

I'm using the 5.2.6 release, and I just hit a gnuplot bug that we
already fixed back in 2017/11:

  https://sourceforge.net/p/gnuplot/mailman/gnuplot-beta/thread/2603217.PItpvUgmjs%40stonelion/#msg36096047

It looks like this fix is in place in the master branch, but not in the
latest release. Is this intentional? Can we release it?

Thanks!