Add ConditionVariable.wait_until and ConditionVariable.wait_for

[cbuttner]

No description provided.

[cbuttner]

I should mention wait_for overlaps with wait_timeout, so maybe wait_timeout could be deprecated.

[lerno]

What about wait_duration rather than wait_for

[cbuttner]

Actually I think wait_timeout is a good name, because it doesn't imply that it guarantees to block for the full duration (it might not due to spurious wakeups).
But how should it take a Duration instead of ms without it being a breaking change?

[lerno]

Well, you can be tricky and use macros for it. But there's a problem with Duration / NanoDuration and just ms because of how they're converted from literals. So for now you need to assume passing "1" means ms and not Duration. But this is a bigger problem, where I wonder if typedefs should be able to opt out of implicit literal conversion.

[lerno]

I modified so that timeout worked for either, allowing us to deprecate ms later.

[lerno]

Thank you!