-// GRG, Dic/99
-// Computes the histogram of the image and fills a hash table, indexed
-// with integer keys built as 0xRRGGBB, containing wxHNode objects. Each
-// wxHNode contains an 'index' (useful to build a palette with the image
-// colours) and a 'value', which is the number of pixels in the image with
-// that colour.
-//
-unsigned long wxImage::ComputeHistogram( wxHashTable &h )