Cleaned up HEAD for the upcoming, completely rewritten version of the CDN integration module. This rewrite was part of my bachelor thesis.

- Improved: permissions added to access per-page statistics. Refactored hook_file_server() implementation and cdn_file_url() to use less memory.
- Improved: added a debug mode, in which only users with a certain permission get served files from the CDN.

- Added a check for PHP's safe mode in hook_requirements().

- Improved: list file counts in each of the 3 sections of the site-wide statistics.

Fixed: when unique method is set to "none", cdn_unique_filename() would return nothing, instead of simply returning the file path it received. Darn typo.

- Fixed: some file paths with relative URLs would result in empty urls in CSS/JS files (i.e. when the "update urls in files" option is enabled for a filter). This was because I was not yet actually *resolving* the relative references (double dots) in the file paths.
- Improved: removed an obsolete parameter from the cdn_file_url() function.

- Updated the example configuration.

- Fixed site-wide coverage percentage calculation.
- More consistency in output of site-wide statistics.

- Updated the module to use the new hook_file_server() provided by the core patch.

- Abstracted the cdn_file() function to an "URL rewrite function" for core usage. This will allow you to have any number of backends to serve files from. Updated the core patches, the documentation and the code accordingly.

#212376: implemented #3: Ability to choose either Drupal's cron or CDN integration's cron as the cron method.

Improved the per-page statistics a lot, as well as the side-wide statistics. They are much more helpful now in tracking down files that aren't being picked up by your filters.

- Improved: files that /are/ being synced are stored in a temporary variable, which are then used when updating files (e.g. CSS files). This is necessary to properly update files; to use the latest files available on the CDN.
- The core patch without JS aggregation was not yet updated properly.