Gnuplot development version is now 5.3

[Ethan A Merritt]

I have bumped the version number of the development source to 5.3.

No change to your cvs setup is necessary, but you may need to do
a complete "make install" for testing because the directory path
for shared files and executables is now /usr/local/share/gnuplot/5.3
rather than /usr/local/share/gnuplot/5.1 and so on.

The status of the stable version remains unchanged.
5.2.rc1 testing has turned up a couple of bugs that affect normal use.
Extensive fuzz-testing has turned up a somewhat larger number of bugs
that can be triggered only by erroneous input commands or data.
All of these have been fixed in the stable and development cvs source.

My plan is to put together an -rc2 test package at the beginning of July.
If there is anything not already in cvs that you would like to see
included in -rc2 please let me know.

Ethan