MFC: Quota system cleanup & disallow negative ids when accouting for
quota usage.

ffs/ffs_alloc.c rev 1.143
ffs/ffs_snapshot.c rev 1.132
ufs/quota.h rev 1.29
ufs/ufs_quota.c rev 1.86 - 1.88
ufs/ufs_vfsops.c rev 1.48