Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

err() takes a printf format.

Submitted by: Pawel Worach
Spotted by: clang

Add wtmpcvt(1).

This utility allows users to convert their wtmp databases to the new
format. It makes no sense for users to keep their wtmp log files if they
are unable to view them.

It basically copies ut_line into ut_id as well. This makes it possible
for last(1) and ac(8) to match login records with their corresponding
logout record.