Build failure with rust nightly

[chandraprakash]

rustc 1.2.0-nightly (2f5683913 2015-06-18)

[vinipsmaker]

This recent build failures comes from two sources:

• We should use #![feature(arc_weak)] now.
• scoped was deprecated.
  • The reason behind deprecation is old.
  • This post is a good reading on the problem.
  • The discussion still heated and I'm not sure they'll provide a replacement soon.
    • So, I'm going to replace all scoped usages with spawn.

[chandraprakash]

+1 .. Thanks Vinícius

[vinipsmaker]

Previously, join couldn't fail, but outside of the scoped API, this scenario might happen.

I couldn't easily convert Err(Box<Any + Send + 'static>) to Err(std::io::Error), so I used unwrap for now. Possibly I'll refactor to use some adapter (e.g. Err(Error::new(Other, /* ... */)) or change BroadcastAcceptor::accept return type. These solutions touch public interface and I would need some time to make sure I don't break anything, but I was told you guys are in a hurry to getting this thing building for now, so I used unwrap.