Connect asynchronously

[igorw]

Currently the connect call itself is blocking.

We should call stream_socket_client with the STREAM_CLIENT_ASYNC_CONNECT flag. But that means we cannot tell connection failure at connect time.

We can only detect connection failure if we have reactphp/reactphp#113. So that needs to be fixed first.

[nrk]

There's a workaround even without the need for reactphp/react#113: you set the STREAM_CLIENT_ASYNC_CONNECT flag and subscribe for a write event on the connecting stream, if stream_socket_get_name($socket, true) === false when the write event kicks then it means that the connection has been refused.

I do that in Predis\Async and it seems to work quite well, see here and here for the related code.

[igorw]

That's quite nice, ideally we would have something for that in react core.