Fix various problems with recovery and log archiving:
- only set the checkpoint LSN for full checkpoints,
- close all handles used by the WT_LOGSCAN_RECOVER flag,
- only backup "active" log files -- not ones that can be deleted at any time by the log archive thread.
Bound the start LSN during recovery to the available log files.

The common case is that some files were not dirty during checkpoints, so the LSN of their last checkpoint is no longer valid.  This is not a long term solution: we need to distinguish when required log files are missing during recovery.