Version 4.0.6

   * sql/database.lisp: Fix syntax on process-lock (thanks to
   Stian Sletner)
   * db-mysql/mysql-sql.lisp: Allow use of database parameter
   in database-list function (thanks to Michael Pheasant)
   * sql/oodml.lisp: Allow NULL values for floating-point fields
   (thanks to Jan Rychter)