Segmentation Features;

Segmentation Features;

Only encode sign bit for feature data that can have a sign.

Tweaks to the test segmentation rules so that it now actually gives
a net benefit on the derf set of about 0.4% though much higher
on some clips at the low end.

Change-Id: I8e61f1aebf41c9037db7e67e2f8975aa18a0c986