title: Slashes (`/`) in CSS values when using Less (e.g. in `font` shorthand)
body: <p>i noticed an issue when using Less with font shorthand</p>
  
  <pre><code>.font(@weight: 300, @size: 22px, @height: 32px) {
      font: @weight @size/@height "Helvetica Neue", Arial, "Liberation Sans", FreeSans, sans-serif;
  }
  </code></pre>
  
  <p>the above fails with</p>
  
  <pre><code>this.a.toCSS is not a function
  http://localhost/tumblr/modern1/css/style.less on line 1, column 0:
  1. @highlight: #cb1e16;
  2. @shade1: #cb1e16;
  </code></pre>
  
  <p>when i split the properties up it works</p>
  
  <pre><code>.font(@weight: 300, @size: 22px, @height: 32px) {
    font-weight: @weight;
    font-size: @size;
    line-height: @height;
    font-family: "Yanone Kaffeesatz", "Helvetica Neue", Arial, "Liberation Sans", FreeSans, sans-serif;
  </code></pre>
  
  <p>}</p>
  
  <p>i think its because of the slash / thats causing the problem, i think since Less can do calculations, eg. <code>2px + 5 = 7px</code> its trying to do a divide?</p>