This 2-pass rate control setting allocates bits based
on first pass stats to each kf group, gf group and individual
frame but does not correct the bits left and allocation after
each frame.

In other words it recommends a bit allocation for each frame
but does not try and correct any over or under spend on a
frame over the remainder of the clip. This reduces the accuracy
of rate control in terms of hitting an average bitrate but prevents
problems that may arise because early frames either use to many
or too few bits. This mode is currently more inclined to undershoot
than overshoot (particularly at higher data rates).

Also minor changes to rate of adaption when recode loop is not
enabled.

This mode is currently enabled by default for VBR.
It gives the following % performance gains.

derf +0.467, +1.072
yt 2.962, 2.645
stdhd 1.682, 1.595,
yt-hd 2.3, 2.174

Change-Id: I3c84a9bf8884e5b345698ff0e19187f792c2f3a0