bart state file error handling

[kmjonsson]

Mail from: Pär Lindfors (Andersson) ([email protected])

bart-logger does not handle corrupted state files very well.

I ran into two bugs while testing the Maui backend together with Moab
log files.

To trigger the first bug I had been stupid and corrupted my statefile
manually.

The second bug I triggered when I changed MAUI_DATE_FORMAT for Moab
compatibility. Another way to trigger this would be if a site purges old
Maui event files too frequently, and removes the file before running
BaRT again. (This would of course also result in missing records, so
perhaps not the best example)