Fix circular reference for redirects (reverts #204)

What thought as a simple precaution against a non-updated redirect #204 (which might have been caused by a MW issue outlined in #212) can create a circular reference.

- Create page `A` to `#REDIRECT [[B]]`
- Create page `B` to `#REDIRECT [[C]]`
- Create page `C` to `#REDIRECT [[A]]`

Above schema will create an infinite `UpdateJob` Queue (tested with `$wgJobRunRate = 0.01;`).

See also [0].

[0] http://wikimedia.7.x6.nabble.com/MediaWiki-Job-queue-problem-tp5036690p5037600.html