Bug 1041712 Fix holes in release notes redirects

* Fix missing trailing slash on buglist.html redirects
* Fix redirects for beta releases

More details: https://bugzilla.mozilla.org/show_bug.cgi?id=1041712#c19
Good catch, sorry I missed this earlier. I think the beta needs to be optional so that the regex will still match non-beta versions. You might also consider making it a non-capturing group within a group you're already capturing to slightly simplify the target like we did on some of the other redirects a few lines above, but that's optional. Maybe something like this:

`RewriteRule ^/(\w{2,3}(?:-\w{2}(?:-mac)?)?/)(firefox|mobile)/([0-9]|1[0-9]|2[0-8])\.([\d.]+(?:beta)?)/releasenotes/(.*)$ http://website-archive.mozilla.org/www.mozilla.org/firefox_releasenotes/$1$2/$3.$4/releasenotes/$5 [L,R=301]`