font-face->src->url() problematic without quotes

[brettz9]

The following causes language-less to choke on the lack of quotes:

@font-face {
  src: url(http://example.com/font.woff) format('woff');
}

url() is not a problem outside of @font-face however, as the following works fine:

a {
    background-image: url(http://example.com)
}