* etc/NEWS.unknown: Add approximate version records for
defsubst, mark, nreverse, let*, rassq, >=,
transpose-sexps, buffer-modified-p, current-column, downcase,
previous-line, catch, throw, and count-lines,
which all were given much more recent introduction versions
by describe-function.
It is not intended for the human reader, but to give less wrong versions
of first appearance displayed by `describe-function` or
`describe-variable` that would otherwise be derived from a notice in a
more recent NEWS* file.
It is better to add items to this file than changing historical NEWS*
files when the actual version of introduction is not known.
* etc/NEWS.unknown: New file. Add entry for `nthcdr`.