update rust

Update to last version.
As far as I can see that part of the code is still there, even when using the same git commit that you are updating to:

```
$ git log | head -n 4
commit 3edcdbb0c01187a0cc6456ca29cd858579459b18
Merge: 0d94fda 942bed7
Author: bors <bors@rust-lang.org>
Date:   Mon Oct 6 14:57:19 2014 +0000

$ tail -n +50 src/librustc_back/archive.rs | head

fn run_ar(handler: &ErrorHandler, maybe_ar_prog: &Option<String>,
          args: &str, cwd: Option<&Path>,
          paths: &[&Path]) -> ProcessOutput {
    let ar = match *maybe_ar_prog {
        Some(ref ar) => ar.as_slice(),
        None => "ar"
    };
    let mut cmd = Command::new(ar);