Shifter chokes on comment containing "Y.log"

[gzip]

Started looking at this with @caridy. Create the following two files and run shifter.

build.json

{
    "name": "debug",
    "builds": {
        "module": {
            "jsfiles": [
                "./js/debug.js"
            ]
        }
    }
}

js/debug.js

YUI.add('debug', function (Y, NAME) {
    function Debugger() { }
    Debugger.prototype = {
        debug: function () {
            // using Y.log's warn level
            if (true) {
            } else {
            }
        }
    }
});

It errors out with the following:

shifter [err] compression failed
       Unexpected token punc, expected punc // line 9, pos 15

Remove or modify the comment and it's successful.