Add regression test for installing empty files.

Address des@'s review: Use putenv() instead of duplicating the work.

Address des@'s comment: Move application of PAM environment to a better place.

I think what bz@ really wanted is something like:

The current logic looks like it was effectively rounding the elapsed time to the nearest hour (with a 30-minute bias). That means a file only 30 minutes old could be considered "1 hour old," which isn’t what a user would normally expect if they configured rotation every hour. A user would reasonably expect “1h” to mean exactly 60 minutes, with perhaps a small tolerance for cron jitter or a slow rotation run.

I like the change in general, but if I was you I'd probably use getopt_long() and call the option --signal (consider this as an optional suggestion; I don't have strong opinion with this choice), because -I was somewhat counterintuitive to me as a flag to specify signal and both -s and -S were already occupied.

For those examining the history of newsyslog(8) and the removal of the -c command-line option, I feel it's important to understand the underlying design philosophy that motivated this and related changes. The goal was to establish a more robust, flexible, and administrator-friendly configuration model.