Fix a bug that crash neko when it runs many async test cases.

[terurou]

Fix #73 .

It makes this code work in neko.

class Main extends buddy.SingleSuite {
    public function new() {
        describe("test", {
            for (i in 0...1000) it("should pass", function (done) done());
        });
    }
}

And It makes to be able to use haxe.Timer.delay() in neko.

[ciscoheat]

Thank you again! How does this work?

[terurou]

In the old code,

• The async tests are run in other thread that is created by AsyncTools.wait(). AsyncTools.wait() creates a new thread each time on neko, so many async test cases crash neko.
• The main thread waits testsDone (all async tests completion) using the while statement. So the main thread is busy, and other statements can't run in the main thread.
• haxe.Timer.delay() doesn't work, because that is implemented using haxe.MainLoop (and haxe.EntryPoint). haxe.MainLoop runs in the main thread. (Maybe haxe.MainLoop can run in any thread, but I couldn't success it.)