Add test for async asserts in subtests ref #42

It passes on this branch with no changes, w00t

test/subtest_and_async.js

@@ -0,0 +1,23 @@
+var test = require('../');
+
+var asyncFunction = function (callback) {
+  setTimeout(callback, Math.random * 50);
+};
+
+test('master test', function (t) {
+  t.test('subtest 1', function (t) {
+    t.pass('subtest 1 before async call');
+    asyncFunction(function () {
+      t.pass('subtest 1 in async callback');
+      t.end();
+    })
+  });
+
+  t.test('subtest 2', function (t) {
+    t.pass('subtest 2 before async call');
+    asyncFunction(function () {
+      t.pass('subtest 2 in async callback');
+      t.end();
+    })
+  });
+});