Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Replace utxrm(8) by utx(8).

At first, I added a utility called utxrm(8) to remove stale entries from
the user accounting database. It seems there are cases in which we need
to perform different operations on the database as well. Simply rename
utxrm(8) to utx(8) and place the old code under the "rm" command.

In addition to "rm", this tool supports "boot" and "shutdown", which are
going to be used by an rc-script which I am going to commit separately.

Add a utility, utxrm(8).

Most of the ports I broke when I imported utmpx, were simple management
utilities for the utmp database, allowing you to add/remove entries
manually.

Add a small tool called utxrm(8), which allows you to remove an entry
from the utmpx database by hand. This is useful when a login daemon
crashes or fails to remove the entry during shutdown.