string length() does not give iterable item count

This works:

```
julia> ["xyz"...]
3-element Char Array:
 'x'
 'y'
 'z'
```

This segfaults:

```
julia> ["é"...]
Segmentation fault (core dumped)
```

My guess is that `[x...]` should use `strlen` instead of `length` in this case.
