`new()` for `Vec<T>` requires type information

Currently, we need to write: 
```rust
let vector = ~Vec::new::<u8>();
```
The type annotation `u8` has to be supplied to `new()`. The following, however, doesn't work:
```rust
let vector: Vec<u8> = ~Vec::new();
```
The second syntax is a bit more intuitive to users and should probably work.