Add test for issue #161.

tests/issue-161-multiple-joiners.d

@@ -0,0 +1,31 @@
+/+ dub.sdl:
+	name "tests"
+	dependency "vibe-core" path=".."
+	debugVersions "VibeTaskLog" "VibeAsyncLog"
++/
+module tests;
+
+import vibe.core.core;
+import vibe.core.log;
+import vibe.core.sync;
+import core.time;
+import core.stdc.stdlib : exit;
+
+
+void main()
+{
+	setTimer(5.seconds, { logError("Test has hung."); exit(1); });
+
+	Task t;
+
+	runTask({
+		t = runTask({ sleep(100.msecs); });
+		t.join();
+	});
+
+	yield();
+
+	assert(t && t.running);
+
+	t.join();
+}