Two pass rate control code changes.

This comitt brings accross changes from the public branch
commit number Icf74d13af77437c08602571dc7a97e747cce5066.

The main puurpose of this comit relates to CQ mode but it
also includes some refactoring of the two pass code which
I hope will make tuning the experimental branch for the new
quantizer range a little less painfull.

Change-Id: I278e989436a928fc1fe7761068960048f9d7a376