This patch implements pre-initialisation of contexts
for the arithmetic coding of wavelet coefficients. For
CIF video sequences at QF 5 this has been shown to
give a coding effficiency gain of around 1%. Instead of
1/2, contexts are initialised to a fraction with a
denominator of 32, based of observations from a large
number of sequences. The initialisation values depend
on frame type, component, subband and context.
Changes are made to the classes ArithCodec, BandCodec,
LFBandCodec, IntraDCBandCodec, CompCompressor,
CompDecompressor and FrameDecompressor.