Pass the current version to the search

From a UX POV, when I'm searching docs I'm likely to be working on a site of a specific version - results of docs from older or newer versions are likely to be less relevant to me. 

If I want to search wider after my initial search I can use the check boxes on the advanced search.

I feel it's a reasonable assumption that a search when I'm on a specific version should return results from that version only.