Handle fallout in os

os::env(), os::args(), and related functions now use Vec<T> instead of
~[T].
Handle fallout in io::net::addrinfo, io::process, and rt::rtio

API Changes:

- get_host_addresses() returns IoResult<Vec<IpAddr>>
- Process.extra_io is Vec<Option<io::PipeStream>>
Handle fallout for vector addition

Adding two vectors now results in a Vec<T> instead of a ~[T].

Implement Add on Vec<T>.
Handle fallout in libserialize

API Changes:

- from_base64() returns Result<Vec<u8>, FromBase64Error>
- from_hex() returns Result<Vec<u8>, FromHexError>
- json::List is a Vec<Json>
- Decodable is no longer implemented on ~[T] (but Encodable still is)
- DecoderHelpers::read_to_vec() returns a Result<Vec<T>, E>
Handle fallout in librustc
Handle fallout in libnative

API Changes:

- GetAddrInfoRequest::run() returns Result<Vec<..>, ..>
- Process::spawn() returns Result(.., Vec<..>), ..>
Clean up unused imports
Handle fallout in librustuv

API Changes:

- GetAddrInfoRequest::run() returns Result<Vec<..>, ..>
- Process::spawn() returns Result<(.., Vec<..>), ..>
Handle more fallout

os::args() no longer auto-borrows to &[~str].
Handle fallout in documentation

Tweak the tutorial's section on vectors and strings, to slightly clarify
the difference between fixed-size vectors, vectors, and slices.
Handle fallout in bench tests