search.css not included when CSS aggregation is turned on

When CSS aggregation is turned on, the search.css stylesheet is not included on search404 results page.

Looks like the cause of this is that the code to include the stylesheet on the results page is still using the D6 api. Passing 'module' as the stylesheet type breaks the aggregation.

I'm attaching a patch that uses the default D7 function call. The original code turned off preprocessing of the stylesheet for aggregation but I'm not sure what the reasoning was for that. Obviously the maintainer is free to add that back in :)