Add recv_timeout for pipes

[eholk]

This seems useful. Part of #1255

[bstrie]

If libuv is intended to provide the timer, then this should wait until brson finishes the scheduler overhaul.

[graydon]

Visiting for triage. Still in the process of transitioning to the new RT but it does not look like anyone's written a recv_timeout variant yet. Possibly you can fake it pretty easily with timer and select, but nothing high level.

[flaper87]

I'll work on this

[flaper87]

I think this still needs to be implemented. @alexcrichton Implemented oneshot and periodic as part of alexcrichton@7a1d97e but those methods don't block the task and messages will be received just after msecs.

[pnkfelix]

Accepting P-low.

[steveklabnik]

I'm pulling a massive triage effort to get us ready for 1.0. As part of this, I'm moving stuff that's wishlist-like to the RFCs repo, as that's where major new things should get discussed/prioritized.

This issue has been moved to the RFCs repo: rust-lang/rfcs#821