Setting CacheDir in site.ini to an absolute path prevents ezjscore (jspacker) from outputting correct URIs.

With DFS the URI is invalid (leading '//'), so the resulting URL uses the first path component as server.

Steps to reproduce

• in site.ini, use an absolute path for CacheDir (under [FileSettings]):
• clear cache

Generated URIs for css and javascript files generated from ezjscore are now invalid.

• With DFS, the generated URI is:
  //var/www/ezpublish/cache/public/stylesheets/file_name.ext
  The resulting URL uses "var" as the server component - http://var/<uri>

• Without DFS the URI is: /var/www/ezpublish/cache/public/stylesheets/file_name.ext
  The URl is valid but with cache path incorrect relative to EZROOT>