The overall goal here is to make readline more interoperable with other node
Streams like say a net.Socket instance, in "terminal" mode.
See #2922 for all the details.
Closes#2922.
This makes it so that the stdin TTY-wrap stream gets ref'ed on
.resume() and unref'ed on .pause()
The semantics of the names "pause" and "resume" are a bit weird, but the
important thing is that this corrects an API change from 0.4 -> 0.6
which made it impossible to read from stdin multiple times, without
knowing when it might end up being closed. If no one has it open, this
lets the process die naturally.
LGTM'd by @ry
