Add get_opt to std::vec
rc: fix docstring
auto merge of #9825 : thestinger/rust/rc, r=thestinger
librustc: Don't ICE on packed structs in statics.
Update test for packed structs to also test being placed in statics.
auto merge of #9608 : hmarr/rust/vec-get-opt, r=huonw

This adds `get_opt` to `std::vec`, which looks up an item by index and returns an `Option`. If the given index is out of range, `None` will be returned, otherwise a `Some`-wrapped item will be returned.

Example use case:

```rust
use std::os;

fn say_hello(name: &str) {
  println(fmt!("Hello, %s", name));
}

fn main(){
  // Try to get the first cmd line arg, but default to "World"
  let args = os::args();
  let default = ~"World";
  say_hello(*args.get_opt(1).unwrap_or(&default));
}
```

If there's an existing way of implementing this pattern that's cleaner, I'll happily close this. I'm also open to naming suggestions (`index_opt`?)
librustc: Combine C_struct and C_packed_struct.
auto merge of #9832 : luqmana/rust/sps, r=alexcrichton

Fixes #9830.
fix typos in doc/tutorial.md
auto merge of #9836 : eriklyon/rust/doc-typos, r=alexcrichton
std::libc: rustdoc indicates reexports now