Type inference doesn't work well with Iterators (0.11.0)

Example code:

use std::iter::AdditiveIterator;
fn main() {
    let x: [u64, ..3] = [1, 2, 3];
    println!("{}", range(0, 3).map(|i| x[i]).sum());
}

In this case, the type of the integers for the range is unambiguously uint, although the compiler still throws an error and won't accept the code unless you add a u suffix to either the 0 or the 3 in the range. This seems to apply to all types of iterators as well, and the compiler isn't good enough to infer the type based upon a later function call in the chain.

[emberian]

cc @nikomatsakis

This is working as intended now but needs a test case.