Adding include paths to CLI testrunner

I think it would be useful to have something like --include=PATH for the CLI testrunner. That way you can setup your testsuite without having to know about the actual location of the test suite in the directory structure. The call to the CLI testrunner then can take care of setting up the enviroment using --include. No need to repeat

```
require =("../lib/LibrarySubjectToBeTested");
```

but do

```
require('LibrarySubjectToBeTested");
```

and simply call

```
nodeunit --include=../lib/
```

I implemented a patch that would add this functionality to the testrunner. Have a look at it: 1db0b284d70829d4fe5f8a1fe20274562cdc5bd8
Please let me know what you think and if there's anything I missed. If you like it, feel free to pull it in.

まず commit 1db0b284d70829d4fe5f8a1fe20274562cdc5bd8 と CLI testrunner のエントリーポイントを確認します。提案されている --include=PATH オプションがモジュール検索環境をどのように設定するかを確認し、その後、既存のテストスイートを実行します。nodeunit --include=../lib/ で相対パスなしに LibrarySubjectToBeTested を require できれば完了です。

索引モデルが issue の本文から書いたものです。