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)

Bump WARNS where possible.

Checked by: make universe
Approved by: ed (co-mentor)

Remove mqueuefs from LINKS, it is no longer needed for nmount interface.

Noticed by: rodrigc

Change filesystem name from mqueue to mqueuefs for style consitent,
sort LINKS list.

Support mounting POSIX message queue filesystem.

style.Makefile(5):
Use WARNS?= instead of WARNS=.

Default to WARNS=2.
Binary builds that cannot handle this must explicitly set WARNS=0.

Reviewed by: mike

Rename (after a repo-copy) some mount(8) programs:

mount_fdesc -> mount_fdescfs
mount_null -> mount_nullfs
mount_portal -> mount_portalfs
mount_umap -> mount_umapfs
mount_union -> mount_unionfs

- Backout botched attempt to introduce MANSECT feature.
- MAN[1-9] -> MAN.

Set the default manual section for sbin/ to 8.

Retire kernfs (userland part).

Add mount_linprocfs.

Removed definition of _NEW_VFSCONF. The new vfsconf interface is now
the default.

Update to compile under Lite2

Now that all of the "standard" file system mount commands
refer the reader to the detailed information in section 5,
remove the mount_* man pages for those file system. mount_std(8)
to cover all of the file systems it is currently being used
to mount.

mount_{devfs, fdesc, kernfs, procfs}.8 are now
MLINKS to mount_std.

Get rid of the last vestiges of the old MOUNT_* constants in the
mount_* programs. While we're at it, collapse the four now-identical
mount programs for devfs, fdesc, kernfs, and procfs into links to
a new mount_std(8) which can mount any really generic filesystem
such as these when called with the appropriate argv[0].

Also, convert the mount programs to use sysexits.h.