make HistogramAdd() a pointer in dsp

* merged the two HistogramAdd/AddEval() into a single call
  (with detection of special case when b==out)
* added a SSE2 variant
* harmonize the histogram type to 'uint32_t' instead
  of just 'int'. This has a lot of ripples on signatures.
* 1-2% faster

Change-Id: I10299ff300f36cdbca5a560df1ae4d4df149d306
10 files changed