Scan through files before the main recovery loop, gathering checkpoint LSNs and file IDs.
Deal with empty metadata during recovery.
Bump the next allocated file ID beyond anything we see during recovery.
Split recovery code in txn_log.c into txn_recover.c.

--HG--
rename : src/txn/txn_log.c => src/txn/txn_recover.c
Add a "recovery" verbose mode.