TEncCU: set dqpflag as true in the CU encoder if aqmode enabled
vbv: set DQP as true if VBV is enabled (and AQ disabled).

Unless this is set, the different QP's for each CU wont be encoded. This worked thankfully
until now, since VBV was always used at high quality (AQ on) settings.
encoder: Adding a TODO comment on the final goal.
compress/TEncCU: no reason why mode decision should reset the dqp flags.
encode: avoid repetitive statements; no logic change
optimize: rewrite TComTrQuant::xGetICRate
optimize: rewrite TComTrQuant::xGetICRateCost
optimize: improvement TComTrQuant::getSigCtxInc, avoid shift by mask
optimize: rewrite TEncSbac::xWriteCoefRemainExGolomb
TComSlice: nits
prevent deadlocks from frame dependencies on Linux

--HG--
branch : stable
Merge with stable