DISCONNECT — close a database connection
Function
errorA boolean flag indicating whether to signal an error 
              if database is non-NIL but cannot 
              be found. 
              
databaseThe database to disconnect, which defaults to the database indicated by *default-database*.
resultA Boolean indicating whether a connection was successfully disconnected.
This function takes a database object as
	returned by connect, and closes the
	connection. If no matching database is found and
	error and
	database are both non-NIL an error is
	signaled, otherwise NIL is returned. If the database is from a
	pool it will be released to this pool.
        
The status of the object passed is changed to closed
        after the disconnection succeeds, thereby preventing further
        use of the object as an argument to CLSQL functions, with
        the exception of database-name and
        database-type. If the user does pass a
        closed database to any other CLSQL function, an error of
        type sql-fatal-error is
        signalled.
The database connection is closed, and the database
	  object is removed from the list of connected databases as
	  returned by connected-databases.
The state of the database object is changed to closed.
If the database object passed is the same under
	eq as the value of
	*default-database*, then
	*default-database* is set to the first
	remaining database from
	connected-databases or to NIL if no
	further active database exists.