Log Message:
gnuplot: updated to 5.2.1

Release 5.2.1

A few bug-fixes present in the distributed package for 5.2.1 are not yet
commited upstream because the repository is in the process of migration
from cvs to git.

* src/graphics.c (plot_betweencurves):
        plot 'foo' with filledcurves below y=bar
would fail to identify "below" regions where the y value foo[x] at the
start or end of the region was exactly equal to bar.

* src/axis.c (gen_tics):  `set log x; set xtics foo` would always place
the first axis tic at foo rather than at (foo / base^N) for suitable N.

* src/win/winmain.c (ConsolePutS, ConsolePutCh):  Use standard file IO
instead of Console API to enable word-wrapping on Windows 10 and to
allow for redirection of stdout/stderr.

* term/post.trm:  Raise the limit on number of relative moves before
a "stroke" so that a full circle as drawn by do_arc() does not glitch
due to insertion of a "stroke xx yy M" sequence that resets the
dot/dash pattern.

* src/plot2d.c (eval_plots): If the range for logscaled y axis is empty,
e.g. the plot holds a single point, auto-extend the range rather than
giving up with an error.