Stacktrace improvements

There is a lot of nodeunit and async.js noise in the stacktraces... If we can _reliably_ improve the stacktraces, it would make debugging failing tests a little nicer.

I'm a bit worried about messing with something as fundamental as a stacktrace, but it might be worth experimenting with, and could be included as an option to the command line tool at first.

See: http://code.google.com/p/v8/wiki/JavaScriptStackTraceApi

该 issue 没有列出文件或测试；请从命令行工具入手，并查看报告中链接的 V8 JavaScript Stack Trace API。完成的标准是可靠且经过实验验证地减少 nodeunit 和 async.js 的噪声，并将任何初始行为作为显式的 CLI 选项公开。

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