Serve flash socket policy file

Read about flash socket policy:

• http://www.adobe.com/devnet/flashplayer/articles/socket_policy_files.html
• http://www.lightsphere.com/dev/articles/flash_socket_policy.html

The protocol to serve flash socket policy file is different from HTTP. To serve:

1. Modify config/flash_socket_policy.xml appropriately
2. Modify config/xitrum.conf to enable serving the above file