The purpose of this daemon is to maintain preset disk quotas by checking how
much disk space a user is using before allowing them to use more.

All commands (except logging) that write to files should call valid_write()
in the master object.  This calls quota_check() in the daemon which
recursively uses get_dir() and file_size() to check how much disc space
the user is currently using.

NB: it does not currently handle links.

On create() it calls load_quotas() which reads in the file /adm/etc/user_quotas
which is where the individual quotas are defined.
The current defaults are 
  Students - 100k
  Wizards  - 200k
  Admins   - unlimited

Documented by Pallando@TMI-2 (93-08-18)
