At eob-1, coefficient must be non-zero. As such, this CL changes the
alphabet for base levels at eob-1 from size 4 to size 3. Minor
performance improvement is observed. In addition, changes in 33462 made
by Ola Hugosson were also incorporated.

Now with trained initial probability distributions.

Change-Id: Id6b5d0908b5ff186ed88ab0733ce7cc0c4a468d5