combine_css should scan for syntax errors to avoid combining broken files

[GoogleCodeExporter]

What steps will reproduce the problem?
1.  Surf to that site
2.  Look scroll down below the main photo
3.  Look at the 55x55 photos

What is the expected output? What do you see instead?

Expected: grid of photos
Found: 3 diagonals of photos

What version of the product are you using (please check X-Mod-Pagespeed
header)?

    0.9.16.9-576

Please provide any additional information below, especially a URL or an
HTML file that exhibits the problem.

http://www.polywood-furniture.com/polywood-adirondack-chair-1.html

Original issue reported on code.google.com by jmara...@google.com on 28 Mar 2011 at 4:36