Bugfix for /js/ and /css/ URLs not being cached when ‘Add Store Code to Urls’ is enabled for all store views

Bugfix for: 
The "check if the request is for part of magento" regex does not match for URLs starting with "/skin/" and "/js/" when a shop has enabled ‘Add Store Code to Urls’ for all store views. 
This causes caching not to work for JS and CSS URLs when a cookie is set.

Please merge my small change to the "devel" branch.