Re-index blob content (files, attachments) that didn't index due to doctotext path

lp:1081104 showed that deployment via Fabric causes the path to doctotext to get lost. This probably means we have a bunch of content that didn't get indexed.

Specs
- Can be run several times
- Avoid production conflict errors, so run in chunks
- Works for File objects and anything with attachments (blog posts, comments)
- Discardable (doesn't need to be a permanent feature of the software)

I propose writing something that can run in karlserve debug. Just a script in /tmp. Throw it away afterwards.

When you run it, it tells you how many have the problem, then reindexes the first 10 or so. You just keep running it manually until done. Alternatively, do subtransactions. Either way, avoid ConflictErrors with the production site.

With this approach (versus an evolve) we don't need to actually deploy software and schedule downtime.