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)

Set magic fbsd:nokeywords property that allows files to bypass
keyword expansion. (file-specific replacement for CVSROOT/exclude)

Sync XFS for FreeBSD tree with newer changes from SGI XFS for Linux tree.
Improve support for writing to XFS partitions.

Work done by: Russell Cattelan <cattelan at xfs dot org>

Cope with -Wundef. This means including xfs_macros.h early in a few more
files and changing #if XXXKAN -> #ifdef XXXKAN.

# this is just compile tested, since I don't have xfs partitions.

Initial import of read-only support for SGI's XFS filesystem.

Contributed by: XFS for FreeBSD project