As for clean_up. This is a function that is called in all objects with
regular intervall. The object have basically three choices:

   1) Destruct itself.
   2) Return 0; Meaning call me again for possible clean_up.
   3) Return 1; Meaning Do not call me again, 'I will never destruct'

What you do with it is entirely up to you. The ONLY place that it is
currently used in the mudlib is in /std/room.c Rooms selfdestruct if
they are empty. If you want another behaviour then make your own clean_up().

