VIP File System performance improvements

We have improved the performance speeds of VIP File System PUT and DELETE requests. Uploads are now up to 5X faster and delete operations are up to 4X faster.

In addition, new global helper functions were added to a8c-files.php in VIP MU plugins: wpvip_fs_local_file_add, wpvip_fs_local_file_remove, and wpvip_fs_local_file_list. These helper functions can be used by WordPress applications to mark files to be handled by the PHP stream wrapper in the local temporary directory rather than being uploaded to the VIP File System.