JSMin compressor fails in some cases

In 5.1.0-RC we have ability to compress css and js files. For JS file compression we use JSMin library, which fails to work on attached file.

I propose, that we use YUICompressor, when java is available on web server and use JSMin, when java is not available.

JAR file must be places together with other minify helpers.

Attached patch adds ability to use YUICompressor.