backgroundImage does not allow spaces in image file name

[Charles1625]

I ran into this problem and then did some investigation. I think the problem is actually in Css.url which needs to put some quotes round the string supplied in the argument. Currently it is returning:
{ backgroundImage = Compatible, value = "url(an image.jpg)" }
when it should be returning:
{ backgroundImage = Compatible, value = "url('an image.jpg')" }