While this implements a standards-conforming C11 function, there's
implementation details the programmer needs to know. Include those
here. Make changes inspired by comments on the initial review as well,
though mostly this involves stealing the epoch verbage from
gettimeofday(2). Add myself to authors since I've now changed a
substantial amount of this man page.
Bring in the functionality for timespec_get from NetBSD. I've lightly
edited the .c file to remove _DIAGASSERT because FreeBSD doesn't have
that functionality and the typical #define'ing it to assert isn't
right here. The man page is verbatim from NetBSD, but will be revised
as part of a larger cleanup of the time man pages (they are
inconsistent and vague in all the wrong places).
Differential Review: https://reviews.freebsd.org/D16649