Update Rust

The Rust version is now at:
```
rustc 1.9.0-nightly (0dcc413e4 2016-03-22)
```

This includes a fix for the following build error that the new version
produced:
```
src/rust_base.rs:17:1: 19:2 error: definition of an unknown language
item: `stack_exhausted`. [E0522]
src/rust_base.rs:17 pub extern fn stack_exhausted() {
src/rust_base.rs:18     panic!("Stack exhausted");
src/rust_base.rs:19 }
src/rust_base.rs:17:1: 19:2 help: run `rustc --explain E0522` to see a
detailed explanation
```

It looks like the `stack_exhausted item was removed last year:
rust-lang/rust#27338

This didn't cause an error so far, because the compiler didn't complain
about defining lang items that don't exist. This seems to have changed
in this pull request:
rust-lang/rust#32264

Author: hannobraun

blink/src/rust_base.rs

@@ -13,11 +13,6 @@ pub extern fn panic_fmt() {
     loop {}
 }
 
-#[lang = "stack_exhausted"]
-pub extern fn stack_exhausted() {
-    panic!("Stack exhausted");
-}
-
 #[lang = "eh_personality"]
 pub extern fn eh_personality() {
     panic!("eh_personality function has been called")