A new command vbackground is created. Old background commands are made aliases for the newly created command (including vsetdefaultbg).
Tests are modified using newly added command vbackground.
Image_Color - removed semibroken summ/difference operators.
Image_Diff now uses signed integer for computing differnce between ubyte3 components;
properly compare squared tolerance.
Image_Diff - dropped declaration of Image_ColorXXX24.
RGB color difference is now computed using Chebyshev distance instead of Euclidean distance
Image_PixMap - added methods RawValue()/ChangeRawValue() returning a pointer
to image where specified pixel data is defined.
tiv