Added in comment filtering to prevent commented scripts/styles from being added into the concat list

// use case
`<!-- 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.