Pre-release source tarball for gnuplot version 6.0

[Ethan A M. <me...@uw...>]

I have placed a pre-release tarball in the testing area on SourceForge

     https://sourceforge.net/projects/gnuplot/files/gnuplot/testing/gnuplot-6.0.0-prerelease-test.tar.gz

Please use this to confirm successful builds or report any problems that might
hit during packaging.

There are three changes to the source since -rc3

- Replotting and mousing multiplots
        o now working much more comprehensively
        o revert "set mouse multiplot" as a separate command; it's now always in effect
- "plot with polygons" now guarantees that the border of each polygon is a closed curve
- pdf output from the cairo terminals now conforms to %PDF-1.5

My thought is that if no problems are reported, I will use the same tarball for the
full release in about 10 days.

happy gnuplotting

	Ethan