process.exit before console buffer flushed in Windows

## Symptoms

If any test fails, not all the console output is shown (console output is truncated).

Problem does not show up in standard Windows `cmd`, but does show up if tests are run from Cygwin or within Sublime Text build system. In Cygwin, if the output is piped to a file instead of being displayed on the console then all the results show in the file, even though they did not show in the console when not piped.
## Environment
- nodeunit 0.9.0,
- node 0.10.17
- Windows 7
## Minimal Example

I have the following test file, `tests.js`:

```
for (var i = 0; i < 30; i++)
console.log('' + i);

exports.dummy = function(test) {
test.fail();
test.done();
}
```

Running from Cygwin, the result is:

```
$ nodeunit tests.js
0
```

(I.e., only the first console.log appears). But if I remove the `test.fail` line then all the output appears.
## Cause

My guess of the cause is given in the title. It appears that under different circumstances, sometimes the node console is _asynchronous_ (perhaps due to the way Windows pipes work, I'm not sure), and doesn't flush the output after every write. When a test fails, [line 130 in nodeunit/nodeunit](https://github.com/caolan/nodeunit/blob/60b7d67250a8005fcca6d71a18697c9bdc6613bd/bin/nodeunit#L130) `process.exit(1);` seems to recognize the error and exit the process, but `process.exit` does not seem to always wait for the console output to be received by the terminal. To confirm this hypothesis, if I remove the `process.exit` line, then the output is displayed correctly.
## Solution

A work-around seems to be to change [lines 128-132](https://github.com/caolan/nodeunit/blob/60b7d67250a8005fcca6d71a18697c9bdc6613bd/bin/nodeunit#L128-132) to the following:

```
testrunner.run(files, options, function(err) {
if (err) {
process.on('exit', function() {
process.exit(1);
});
}
});
```

This seems to produce the correct error code for the process and also show all the output. I don't know if there are any other side effects of not ending the process immediately in the callback function.

从 bin/nodeunit 的第 128-132 行附近开始，尤其是第 130 行的 process.exit(1)，并在 Cygwin 下使用提供的 tests.js 重现该问题。确认失败的运行会显示所有控制台输出，同时仍返回退出代码 1；现有的 workaround 提供了用于验证的预期行为。

由索引模型根据 Issue 内容生成。