can @vector-take-while return the source vector itself, or should it

make a fresh copy anyway?   it's not clear from the srfi text.

To be safe, it should, so that the caller can rely on that the returned

vector is never shared.  If that's the intention, we may amend the spec

as clarification.  Just change "Returns a @vector ..." to "Returns a new @vector ..."

or "Returns a fresh @vector ..." should suffice.

The same applies to:

- @vector-take, @vector-take-right, @vector-drop, @vector-drop-right 

  (when N is the same as the length of the source vector)

- @vector-take-while, @vector-take-while-right, @vector-drop-while,

  @vector-drop-while-right

- @vector-filter, @vector-remove (when no elements are removed)

- @vector-segment (when n is equal to or greater than the length of source vector)