(This version is compatible with 1.0023)

• Stale references (objects blessed into DBM::Deep::Null), which
  have always supposed to act like undef, now compare equal to
  undef, "" and 0. $stale_ref eq "" used to return false, even
  though "$stale_ref" was the empty string.
  
• If you assign a stale reference to a database location,
  DBM::Deep now warns and assigns undef, instead of dying with
  obscure error messages.
  
• Using a stale reference as a hash or array ref now causes an
  error with a more helpful message.