Change speed features / behavior for split mode when there
is an internal active edge (e.g. formatting bars).

Remove some threshold constraints in rd code near the active
edge of the image.

Add some plumbing for left and right active edge detection.

Patch set 5. Limit rd pass through for sub 8x8 to internal active edges.
This takes away any speed penalty for most clips but keeps the enhanced
edge coding for the more critical case of internal image edges

Change-Id: If644e4762874de4fe9cbb0a66211953fa74c13a5