a BDB::Lsn object is created by the method log_checkpoint, log_curlsn, log_flush, log_put
compare 2 BDB::Lsn
same than log_file
same than log_flush
same than log_get
The log_file function maps BDB::Lsn structures to file names
The log_flush function guarantees that all log records whose DBB:Lsn are less than or equal to the current lsn have been written to disk.
return the String associated with this BDB::Lsn
[Validate]