Fixed bug in custom testers

Even when a `canCollapseWhitespace` 'tester' was passed, it was never used. The code in `_canCollapseWhitespace` erroneously refered to `options.canTrimWhitespace`. This change fixes this.
Merge pull request #124 from Larixk/patch-1

Fixed bug in custom testers
Switch to Grunt.
Drop Node.js 0.6 support.
Add banner to dist files.