2.6.x resolved in 63689

In 2.6.0.

I committed this in 63678. I did quite a bit of testing on the oracle side of this. In an unconverted database with old emails in the archive, there are errors thrown as soon as you go to the archive. If you run the conversion old emails do not appear but new emails are inserted successfully. If you run the conversion shell script then old and new emails all appear correctly. So it seemed like it was better to have this as part of the main conversion and have it mostly work (even if someone misses the step about converting old emails) than to not work at all.

Also included is the fix mentioned where the mailarchive indexes can be corrupted. (https://sakaiproject.atlassian.net/browse/SAK-16553#icft=SAK-16553)