new block stuff

Hi!,

    I have rewritten all 'block' stuff.  The older approach was not useful, since we need both
pixel and data blocks ( pixel blocks form SAD/..., and data blocks for transform/quantize/...).

    Please read in 'common/Block.h" the comment about the new names and uses.  I hope
that in a few weeks i can clean up everything a little bit.  Even if there are a few different
types of blocks i hope that their use is clear and easy.  Of course, the high efficiency of the
last version remains the same. 

    /AITOR