In non QWERTY keyboard, pressing S won't focus the search bar.
This commit fixes the problem.
Note that `keyCode` is not supported in IE8 already, so the fact
that `key` is not supported in IE8 too doesn't really matter:
the PR doesn't cause browser compatibility for the features to degrade.
1. Focus on the search box for either "s" or "S"
... accepting only "s" makes sense to me, but the comment said it
accepted "S" and well why not
2. Look for a "keyup" event instead of key press, so that pressing "s"
ONLY focuses on the box and does not focus-and-write-the-letter-"s"
"keyup" events apparently don't have a useful `charCode` field so this
PR looks at the `keyCode` field instead
