If no child process has changed state, waitpid() returns zero. But if there
are no more child processes at all, it returns -1 and sets errno to ECHILD.
Since checkExits calls waitpid() in a loop, it must ignore ECHILD.

+Unit test modified to exhibit the unexpected behaviour.

Make AsyncUnixTest/InterruptedTimer slower on Linux becaues it turns out to be flaky on machines other than mine.

(Later, we should add a nice subprocess API around this, maybe even one that can work on Windows too...)

I prefer #ifdefing out the whole file rather than adjusting every build system.

Warned by gcc 5.3.1 and clang 3.7.0

Make tests work on mipsel, maybe. Hopefully fixes #204. I don't know since I don't have a mipsel machine.

A compatibility layer is provided to ease migration.

This is not currently used, but eventually we'll use this to support efficient inter-thread messaging.

That said, I've decided that inter-thread messaging is complicated and I don't want to work on it right now.

For portions currently copyright by Kenton (most of it), transfer copyright to Sandstorm Development Group, Inc. (Kenton's company).

The license change is practically meaningless, as MIT and BSD 2-clause are legally equivalent. However, the BSD 2-clause license is sometimes confused for its ugly siblings, BSD 3-clause and BSD 4-clause. The MIT license is more immediately recognizeable for what it is.

Rémy Blank and Jason Choy (the two non-trivial contributors) are on record as approving this change:

https://groups.google.com/d/msg/capnproto/xXDd2HUOCcc/gbe_COIuXKYJ

- Define separate times for durations vs. absolute times.
- Make more consistent with existing precedents in KJ style.

Make all Promise methods consistently consume the promise (returning a new promise when it makes sense), rename daemonize -> detach, and make eagerlyEvaluate() require an error handler (this caught several places where I forgot to use one).

Overhaul the way EventLoop is specialized so that it's possible to hook up to an existing event loop infrastructure that is not KJ-aware.  This also makes the async IO API more dependency-injection-friendly.

Revamp concurrency model, part 1:  EventLoop no longer allows cross-thread event queuing, simplifying many things.  Capability clients are no longer thread-safe, so they don't have to be so const.  In the future, explicit ways to communicate between threads will be re-added, but threads will be treated more like separate vats that just happen to have a particularly fat pipe.  Upcoming:  Remove mutexes.

Make EventLoop current when constructed, so that you can use the Promise methods even when the loop hasn't actually started yet.

Add tests for actually receiving multiple signals and multiple polls at once, not just listening for them.