Updates to avoid duplicates in point in time records, which has been causing some problems for some users.

1. Make sure deletions from the temp change log by the change log processor looks at the row count to make sure it wasn't deleted by another process. This wasn't working in Oracle.

2. When processing temp change log records, make sure a committed record doesn't already exist in point in time.

3. Add a unique index to each point in time table. This will be done for new 2.1.3 installations. Current installations will get it when upgrading to 2.2.

4. Add script to find and delete duplicates. This won't work right now if there are foreign keys on the duplicates.