src/video.rs:5:4: 5:22 error: unresolved import: there is no `RngUtil` in `std::rand`

On Rust master branch, get the following error after a fresh clone:

```
$ ./configure

$ make
rustc --cfg image --cfg mixer src/sdl.rc -o libsdl.dummy
src/video.rs:5:4: 5:22 error: unresolved import: there is no `RngUtil` in `std::rand`
src/video.rs:5 use std::rand::RngUtil;
^~~~~~~~~~~~~~~~~~
src/video.rs:5:4: 5:22 error: failed to resolve import `std::rand::RngUtil`
src/video.rs:5 use std::rand::RngUtil;
^~~~~~~~~~~~~~~~~~
error: aborting due to 2 previous errors
make: *** [libsdl.dummy] Error 101
```