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

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

Introduce and use new flag -L to mount for mounting only late filesystems.

Previously, rc.d/mountlate mounted *all* filesystems, causing problems with
background NFS mounts being mounted twice.

PR: conf/137629
Submitted by: eadler (original concept)
Reviewed by: mjg
Approved by: hrs

As previously discussed, add the svn:executable property to all scripts

Don't say we're going to mount filesystems of a certain type unless
there actually are filesystems of that type to mount.

Forced commit to correct previous commit message:

Do nextboot -D twice during boot. The first time in rc.d/root which ensures that
we can remove the file as early as possible, but shut up nextboot at this moment
if the operation is failed, because /boot is not necessarily a part of /; the
newly added second run is placed in rc.d/mountlate after all filesystems were
mounted.

Discussed at: -rc@
Suggestions from: brooks, mtm
MFC after: 1 month

root

The check for errors from the mount command did not work as intended
because another command (echo) is executed between the mount command
and the check.

Reported by: Sergey Baturov <sergey@toor.org.ru>
MFC after: 2 weeks

o Implement the stop_boot subroutine [1]. This subroutine can be used by
scripts in rc.d to stop rc(8) from booting into multi-user mode when
a critical or severe error condition is encountered.

o Modify scripts in etc/rc.d that already implemented this functionality
independently.

o Document it.

[1] - This subroutine was implemented in FreeBSD in rc.d/fsck. I moved it
to rc.subr(8). Our version differs slightly in that it takes an
optional argument to stop the boot even if "autoboot" is not set.

Obtained from: NetBSD
MFC after: 2 weeks

Teach mount(8) about a 'late' keyword, which means the file system should
not be mounted unless the -l flag was specified.

Add an rc script, mountlate, which basically runs 'mount -a -l'. It runs
after DAEMON but before LOGIN.

This is useful for things like loopback mounts, because mountcritremote
runs before mountd / nfsd (since /usr might be a remote file system), so
an attempt to mount a loopback network file system in mountcritremote will
fail.

Also add a progress message to mountcritlocal, for the sake of symmetry
with similar messages in mountcritremote and mountlate.

Reviewed by: freebsd-rc
MFC after: 3 weeks