Use a linear SHUFFLE when supplied with many list items to shuffle

There is a PR at https://github.com/phmarek/alexandria/pull/1 that avoids quadratic behavior of shuffle on lists by resorting to an intermediate vector; should it be merged?

Does anyone realistically depend on SHUFFLE on long lists to not cons? If that is the case, should this branch perhaps be toggled via a keyword argument? EDIT: if someone has a really large list, they already lose with that shuffle, so it's unlikely to me that this change realistically affects someone.