Added in comment filtering to prevent commented scripts/styles from bein...

...g added into the concat list

// use case
```html
<!-- build:js js/vendor/bootstrap.min.js -->
<!--<script src="components/bootstrap/js/bootstrap-affix.js"></script>-->
<script src="components/bootstrap/js/bootstrap-alert.js"></script>
<script src="components/bootstrap/js/bootstrap-button.js"></script>
<!--<script src="components/bootstrap/js/bootstrap-carousel.js"></script>
<script src="components/bootstrap/js/bootstrap-collapse.js"></script>-->
<script src="components/bootstrap/js/bootstrap-dropdown.js"></script>
<script src="components/bootstrap/js/bootstrap-modal.js"></script>
<!--<script src="components/bootstrap/js/bootstrap-scrollspy.js"></script>
<script src="components/bootstrap/js/bootstrap-tab.js"></script>
<script src="components/bootstrap/js/bootstrap-tooltip.js"></script>
<script src="components/bootstrap/js/bootstrap-popover.js"></script>--><!-- requires tooltip -->
<!--<script src="components/bootstrap/js/bootstrap-transition.js"></script>
<script src="components/bootstrap/js/bootstrap-typeahead.js"></script>-->
<!-- endbuild -->
```

In the current implementation all of the above files would be concat'ed together. With this pull request only the scripts/styles that should be concat'ed are, resulting in a smaller files size and less surprise bugs.

Version 2.0 patch related to https://github.com/yeoman/grunt-usemin/pull/76