Planned release of 5.2.4 to correct serious regression in 5.2.3

[Ethan A M. <sf...@us...>]

Dave Horsfall has reported a serious regression in gnuplot 5.2.3 that,
when triggered, causes all logscale coordinates to evaluate as undefined.
This results in empty plots.
Simple reproducer:

    set log y
    plot [1:100] x**2,   1/0 

The underlying error is that the internal flag indicating evaluation of an 
undefined quantity (undefined = TRUE) fails to be reset before the
first plot is drawn.   In the example this is triggered by evaluation
of  "1/0"  as the last thing on the command line but I am sure there
are other ways to trigger it.

I have commited a one-line fix  (undefined=FALSE) to git tip and
to branch-5-2-stable.

The same bug has been in the development version since a year ago
(commit  d7211e24) without being reported, so it doesn't make
logscale axes totally unusable.  Nevertheless it clearly causes a
serious regression so I plan to prepare a 5.2.4 release package this
weekend to correct it.

Several other fixes have been applied since 5.2.3, so the new release
will contain
- a fix for a serious regression in 5.2.3 (spurious evaluation of logscale
  coordinates as UNDEFINED)
- re-implementation of the "refresh" command to correct regressions in
  5.2.0 through 5.2.3
- sanity checks for several invalid command sequences found by fuzzing
- several minor bug-fixes
- two recent minor changes back-ported from the development version


			Ethan