Add checkpoint/redo LSNs to recovery errors.

Hackers,

This patch adds checkpoint/redo LSNs to recovery error messages where 
they may be useful for debugging.

When backup_label is present the LSNs are already output in a log 
message, but it still seems like a good idea to repeat them.

When backup_label is not present, the checkpoint LSN is not logged 
unless backup recovery is in progress or the checkpoint is found. In the 
case where a backup is restored but the backup_label is missing, the 
checkpoint LSN is not logged so it is useful for debugging to have it in 
the error message.

Regards,
-David