djbwares version 4

[Jonathan de Boyne Pollard]

In celebration of the forthcoming leap second, djbwares is now at version 4.

* http://jdebp.eu./Softwares/djbwares/
* http://jdebp.info./Softwares/djbwares/

I've added in the rest of M. Bernstein's public domain libtai library, 
parts of which were already included by some of the tools.  This has 
added the easter, nowutc, and yearcal commands, which are packaged up 
alongside libtai.a, the libtai C language headers, and the libtai manual 
pages in a new libtai package.

More importantly, it has added the leapsecs command, and the 
/usr/local/etc/leapsecs.dat file is now generated from leapsecs.txt 
rather than included as a binary in the source as it was before.  The 
sharp-eyed will also note that support for /usr/local/etc/leapsecs.dat 
(as an alternative to /etc/leapsecs.dat for systems that like 
non-operating system files in /usr/local/etc) has also been added.  The 
leapsecs.txt is the Bernstein 2015-06-30 version (which is still the 
latest published by M. Bernstein) patched with the forthcoming leap second.

The libtai package does not include /usr/local/etc/leapsecs.dat .  
Rather, that is packaged in a separate leapsecs package, to allow 
updated versions to be substituted with ease when they come along, as 
well as to permit installing only that without the rest of libtai.