I did this for three reasons. First, and most importantly, to test this feature I moved one of the critical doctypes into a second index (which is done in the branch I mentioned in the initial PR message). When I did that, search broke for obvious reasons, so I implented this multi index search.

Second, I thought that in [bug 906992](https://bugzilla.mozilla.org/show_bug.cgi?id=906992), Ricky implied that kbforum threads would be included in the main search. Looking back, I see now that he didn't say this, but I still took it as implying that our main search should grow to be flexible enough to search across multiple indexes.

Finally, I didn't know that searching across multiple indexes had a performance impact, though it makes a lot of sense now that I think about it.

If we are ok with limiting the main site search to working only on the critical index (it sounds like we are), then I am ok reverting this back to only searching on a single index. However, I think it would be good to check out the rest of this code with the branch I mentioned above that moves one of the critical doctypes to another index before I revert this change. Otherwise testing gets a little tougher.

:bear: