I can answer 1) and 2) but don't have the skills to write the code for 3).

1) Go to system preferences and click on Date/Time. Set the date to 2012. Close System preferences and hit save. Open Bitcoin-qt and get the corrupted database message. Click abort.
Set system preferences and click set date and time automatically. Open Bitcoin-qt and the database is fine.
2) The database is appearing corrupted to leveldb because the system clock is incorrect.
3) Can you use an atomic clock API and rely on that instead of the system clock to prevent leveldb from becoming corrupted?