[bug 1107621] Show whatsnew for updates to 35.0 betas, when updating from 34

https://www.mozilla.org/en-US/firefox/35.0/whatsnew/?oldversion=34.0 should show the new search /whatsnew template that was added in #2574, but it currently requires an oldversion < 34.0 instead of < 35.0

This PR updates that logic and also adds a couple of extra tests.