don't silently fail in ufs_quotactl()

don't silently fail in ufs_quotactl() if a quotactl() request could not be
satisfied due to the underlying file system being locked. ignoring this error
and returning success has all sorts of ill effects.

ok patrick@ natano@
Allow vfs_quotactl in struct vfsops to be NULL.

Let VFS_QUOTACTL return EOPNOTSUPP when vfs_quotactl is NULL. Adapt
cd9660, udf, fuse, msdosfs, tmpfs and nfs.

ok pedro@
Code changes to clean implicit declarations from libc.

ok patrick@
Remove duplicate entry from hier.7. ok pedro@
Fix VLAN-Priority PCP on vr(4).

The tag layout has one less bit on vr(4), they ignore DEI.

ok pedro@ marco@
Merge pull request #1 from bitrig/master

update to current changes in master