Use `splice` to avoid shifting the other items twice.
Put `extern crate std;` first so it's already resolved when we resolve `::std::prelude::rust_20XX`.
Indents for `cbox` and `ibox` are 0 or `INDENT_UNIT` (4) except for a
couple of places which are `INDENT_UNIT - 1` for no clear reason.
This commit changes the three space indents to four spaces.
