Add a limited-time wait method to Condvar

[sfackler]

For example, in Java: http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#wait(long), or in pthreads: http://pubs.opengroup.org/onlinepubs/009695399/functions/pthread_cond_timedwait.html

[thestinger]

C++11 also provides this, along with some convenience methods taking a closure and doing the necessary loop: http://en.cppreference.com/w/cpp/thread/condition_variable

[sfackler]

It would be nice to have both wait_for(&self, d: Duration) -> Whatever and wait_until(&self, t: Timespec) -> Whatever with one trivially implemented by calling into the other.

[gamazeps]

Looking into it :)