This patch against 2.5.31 cleans up the RingQueue_* functions

- make the buffer length be a power of 2 to speed up index manipulation
- make RingQueue_Dequeue use memcpy() rather than a byte by byte copy
- make RingQueue_Enqueue use memcpy() instead of memmove() as the memory
  regions do not overlap
- Add RingQueue_Flush() and RingQueue_GetFreeSpace()
- make RingQueue_GetLength() an inline