This commit removes the `Handle` argument from the following constructors
* `TcpListener::bind`
* `TcpStream::connect`
* `UdpSocket::bind`
The `Handle` argument remains on the various `*_std` constructors as they're
more low-level, but this otherwise is intended to set forth a precedent of by
default not taking `Handle` arguments and instead relying on the global
`Handle::default` return value when necesary.
This commit is targeted at solving tokio-rs/tokio-core#12 and incorporates the
solution from tokio-rs/tokio-core#17. Namely the `need_read` and `need_write`
functions on `PollEvented` now return an error when the connected reactor has
gone away and the task cannot be blocked. This will typically naturally
translate to errors being returned by various connected I/O objects and should
help tear down the world in a clean-ish fashion.
