bind next-error and previous-error in Occur mode? read-only?

[Drew Adams]

I suppose this is a new-feature suggestion, but it might be considered a bug
;-).

Now that `next-error' and `previous-error' work with `occur', why not bind
them to easy-to-hit keys in Occur mode?

Also, shouldn't buffer *Occur* be read-only? If it were, we could bind `n'
and `p' to `next-error-noselect' and `previous-error-noselect', just as in
buffer *grep*.