Add source map support for Karma's reporter

Hi, this pull request added sourcemap support for karma's rerporter.

It provide readble stacktrace.

Example Project : https://github.com/azu/karma-browserifast-sourcemap

Before

![no sourcemap](http://monosnap.com/image/a5r0rAmW00e5XSbNOBjv2axMgoC7Tg.png)

After

![sourcemap stack trace](http://monosnap.com/image/fMK7enP5w80ZWUcLwSMyELSbFy5cuG.png)

See details on

* https://github.com/karma-runner/karma/blob/master/CHANGELOG.md#v0120-2014-03-10
* https://github.com/karma-runner/karma-traceur-preprocessor/blob/master/index.js#L40
* [feat(reporter): support source maps (rewrite stack traces) · 70e4abd · karma-runner/karma](https://github.com/karma-runner/karma/commit/70e4abd9b8db6b05de557ca6e9204339a21be06b "feat(reporter): support source maps (rewrite stack traces) · 70e4abd · karma-runner/karma")