Revert the patch to check if we've reached end-of-backup also when doing

Revert the patch to check if we've reached end-of-backup also when doing
crash recovery, and throw an error if not. hubert depesz lubaczewski pointed
out that that situation also happens in the crash recovery following a
system crash that happens during an online backup.

We might want to do something smarter in 9.1, like put the check back for
backups taken with pg_basebackup, but that's for another patch.