Cancel async_wait & remove wait_for & wait_until

[klemens-morgenstern]

I have been repeatetly run into issues regarding the timed wait function on posix. I think it might be a good idea to remove them, but add a cancel function that interrupts the async_wait. This would allow a simple implementation of a timed wait without getting into the nitty-gritty of OS behaviour.

[klemens-morgenstern]

I have gotten into even more trouble with the wait_for / wait_until functions on posix, so that I am might now just replace them with an asio::signal_set in boost::process. I am quite certain they should be removed from the proposal, but we will need to insist on async_wait to have a proper replacement (async_wait + timer).

[JeffGarland]

hmm, that's not great as the signal_set isn't part of the networking TS. Not sure how best to address this at the moment, but like you say we're going to need something here.

[klemens-morgenstern]

I think the signal_set is rather easy I think and we have reference code. The bigger problem is installing a signal handler, since that thing is unique accross the process. That might lead to conflicts in big applications.