Add some naive tests for the efun(3) family of debug functions.

Add some tests for pidfile(3).

I want to touch this module to attempt a feature addition but I need some
tests beforehand!

Add testcase from PR/44255, that exercize parsedate(3) with sample
strings taken from the manpage.

Convert the libposix, libprop, librt, libskey and libutil tests to ATF.
Initial work from the GSoC 2008 project by Lukasz Strzygowski.