Add search functionality to repository wikis.

I would like to request an addition to the code search feature referred to in issue #2874.

In my team, we are using the wiki as a sort of triage. Support requests are generally documented with resolution steps in the wiki. However, because of the inability to search the wiki it is proving very difficult.

Therefore, I'd like to request an enhancement to the search functionality referenced in the above issue so that it is extended to also include the wiki for the repository in question.