Making path to bullet.gif in config.css relative to it self instead of absolute.

Making path to bullet.gif in config.css relative to it self instead of absolute.
* Installer has a 'Status of 404 (Not Found)' (/w/skins/skins/vector/images/bullet.gif). Source of this problem is "str_replace( 'images/', '../skins/vector/images/',  );" on line 99 of WebInstallerOutput.php::GetCSS() which transforms this line:
  list-style-image: url(../skins/common/images/bullet.gif);
into this:
  list-style-image: url(../skins/common/../skins/vector/images/bullet.gif);
 all other stylesheets do it relative also, therefor changing this accordingly to:
  list-style-image: url(images/bullet.gif);
But since the installer does not load them directly but includes them from a different path, the str_replace() has been changed from a single replace for both files to two replaces, since they are not both in /vector/ images, config.css is in /common/ and it's images are in /common/images, not /vector/images. Fixed now.