[CSS21] url() parsing

I believe this testcase
   http://test.csswg.org/suites/css2.1/20110323/html4/uri-015.htm

   background: red U\r\4c ("support/swatch-green.png");

is wrong according to the core grammar. But I'm not 100% sure...
Also, we have three passes on the testcase. Do we want the testcase
or the grammar to be right? (I think the grammar should be right
in this case, making this pass probably does more harm than good.)

~fantasai