JIRA assumes buggy CSS handling for uncommon browsers

JIRA serves a different CSS stylesheet for "old" browsers that presumably don't fully support CSS1, like Netscape 4. The actual check for old-browser-ness is:

If useragent is null or (not msie and not moz and not opera)

This means more modern browsers like Konqueror are probably being considered 'old' and fed the old stylesheet. Given the rather minimal browser share of NS4 these days, we can probably drop this check and just serve one CSS to all browsers.