std::rt: Add a standalone sleep function.
Add SharedPort wrapper around rt::comm::SharedPort

SharedPort implementation was missing in std::comm. Since this module
also wraps SharedChan, it makes sense to have SharedPort defined there
as well.
auto merge of #9191 : huonw/rust/are-you-tired, r=cmr

Allows `std::rt::io::timer::sleep(1000)` rather than `std::rt::io::timer::Timer::new().unwrap().sleep(1000)`.
auto merge of #9198 : FlaPer87/rust/shared-port, r=cmr

SharedPort implementation was missing in std::comm. Since this module
also wraps SharedChan, it makes sense to have SharedPort defined there
as well.
Kill off method impls made redundant by default methods.
These impls, at least, can be avoided by deriving Ord.