Commit 393c1c5 ("unix: set non-block mode in uv_{pipe,tcp,udp}_open")
causes a regression in the io.js cluster module.
The io.js documentation states that `worker.send()` and `process.send()`
are synchronous but they no longer were after upgrading to libuv v1.2.1.
The reason they are synchronous is because of backpressure - or rather,
lack of backpressure: a slow consumer eventually causes a fast producer
to run out of memory because the backlog of pending messages in the
producer can grow unchecked.
Ergo, implement uv_stream_set_blocking() on UNIX platforms to let io.js
enable the old blocking behavior for pipes again.
Refs: https://github.com/iojs/io.js/issues/760
PR-URL: https://github.com/libuv/libuv/pull/187
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>
