[PATCH] cache reports invalid URL (full local pathes) when using non default system & temp directories

Drupal outputs invalid URLs for JS and CSS (actually full local pathes) when using cache with non default system & temp directories.
The attached patch fixes that.

How to reproduce :
- go to /admin/settings/file-system
- set "File system path" to eg "/var/www/sites/default/files"
- set "Temporary directory" to "/var/tmp"
- save settings.
- open main main Drupal page (here http://localhost/drupal/)
It's full of invalid URIs, that is full pathes concatenated to relative URLs such as:

note the invalid /drupal//var/www/sites/default/files path that should have been /drupal/sites/default/files
(resp //var/www/sites/default/files instead of //sites/default/files for a site directly at /)

This is because:
- in such configurations, modules/locale/locale.module::locale_update_js_files store full pathes
- modules/locale/locale.module::locale_update_js_files then:
o just use these full pathes,
o pass them to includes/file.inc::file_create_path() which prepend drupal
URI (here /drupal/) before (since the full path is not part of drupal install path)
o calls includes/common.inc::drupal_add_js() which then output these invalids
URLs in the web page