[racket-dev] first and rest in racket/base

I just got tripped up, again, trying to traverse a list with `first' and
`rest' in a `racket/base' file. `first' and `rest' are only available in
`racket' and `racket/list', but not in `racket/base'.

If we want to encourage use of `first' and `rest' over `car' and `cdr'
and of `racket/base' when possible (which, e.g., the style guide does),
I think it makes sense to provide `first' and `rest' in `racket/base'.

The attached patch implements that change.

Does this sound reasonable?

Vincent