Code review comment for lp:~xanderfomin/midori/fix-bug1258849

There's a flaw here: any existing values already stored in user config files will be wrong after this change and anyone programatically dealing with it will be up for a surprise. So I'd rather this were a strictly UI related solution. This already hard-codes "zoom" as a special-case so it may as well deal with 1.0 being 100%?