Sync with upstream r315983.

Move files originating from upstream below "dist/":

OPENSOLARIS.LICENSE -> dist/OPENSOLARIS.LICENSE
usr.sbin/zdb/zdb.8 -> dist/cmd/zdb/zdb.8
sbin/zfs/zfs.8 -> dist/cmd/zfs/zfs.8
sbin/zpool/zpool-features.7 -> dist/cmd/zpool/zpool-features.7
sbin/zpool/zpool.8 -> dist/cmd/zpool/zpool.8
include/libintl.h -> dist/head/libintl.h
include/stdio_ext.h -> dist/head/stdio_ext.h
include/thread.h -> dist/head/thread.h
sys/kern/callb.c -> dist/uts/common/os/callb.c
sys/kern/fm.c -> dist/uts/common/os/fm.c
sys/sys/extdirent.h -> dist/uts/common/sys/extdirent.h
sys/sys/isa_defs.h -> dist/uts/common/sys/isa_defs.h
sys/sys/procset.h -> dist/uts/common/sys/procset.h
sys/sys/sysmacros.h -> dist/uts/common/sys/sysmacros.h

Adapt "usr.sbin/fstyp/Makefile".