(bug 8068) New __INDEX__ and __NOINDEX__ magic words allow control of search engine...

(bug 8068) New __INDEX__ and __NOINDEX__ magic words allow control of search engine indexing on a per-article basis.  Remarks:
* Currently __INDEX__ will override __NOINDEX__ regardless of their relative positions, due to the way things are written.  Instead, the last one on the page should win.  This should be pretty easy to fix.
* __INDEX__ and __NOINDEX__ override $wgArticleRobotPolicies.  This is almost certainly incorrect, but it's not totally obvious how to fix it, because of the way the code is structured.  Probably not a big deal, but should probably be fixed at some point.
* Anyone can add and remove the magic words, and there's no config option to disable them.  It's not obvious whether this is okay or not.  It would be a one-line change to OutputPage.php to have a config option to ignore the magic words, maybe per-namespace or who knows what.