Update the tools to support 4x4 TF'd neighbors.

Add TF_BLOCKS global flag so that intra_pred, intra_stats and intra_trace
 all default to using neighbors that have been TF'd down to 4x4 blocks.
encoder: add --enable-encoder-check option

With this option enabled, the encoder will decode its encoded
packets and compare them against its reconstructed frames.

Signed-off-by: Nathan E. Egge <negge@dgql.org>
encoder_example: remove dead code

video_ready is always true at this point.