Added a basic thumb-handler.php file, configured via thumb.config.php. The code is...

Added a basic thumb-handler.php file, configured via thumb.config.php. The code is based on the wmf thumb handler, but simplified. It is disabled by default.
* The thumb.php parameter extraction can also be overridden by the config to handle more complex setups and things like OggHandler and PagedTiffHandler.
* A simple 404 error page is also included. It can be overridden by the config.
* Additional HTTP headers can be passed through cURL via the config.