Skip the last frame update for some frame repeats.
Where a frame appears to be a repeat of an earlier frame or frame buffer, but the first pass code does not anticipate this (usually because it is matching the GF or ARF buffer not the last frame buffer), do not update the last frame buffer. This helps ensure that the content of the last frame buffer is kept "different" where possible, and not updated to match the GF or ARF. This is particularly helpful in some animated sequences where there are groups of repeating frames. Here it has quite a big impact. However, in most of our standard test clips it has little or no impact. Change-Id: I77332ee1a69f9ffc0c6080bfeb811c43fd8828e6