This should have been done long ago. Now it is being done.
This also changes ar_text_id to NOT NULL, since it should never be null
anymore, and DEFAULT 0 in preparation for MCR stopping writing it.
Bug: T33223
Change-Id: I18f1c740b7537c7dc3cfeba9b241d0a9f31caa34
Revisions deleted before MediaWiki 1.5 do not have a value in this
field. This is going to be a problem for migration to the MCR schema, so
provide a maintenance script to clean this up.
Then, for good measure, change the schema to make the field
non-nullable.
Bug: T182678
Change-Id: Ie2e11f12a30f379db32c3e074658012c6f93adb0