A new class Image_Diff for comparison of images
and a draw-command "diffimage", which compares 2 images.
Image_PixMap redesigned to provide interface for low-level image operations.
New Image_AlienPixMap class now intended for Save/Load functionality.
Aspect_PixMap class dropped.
Xw_PixMap and WNT_PixMap classes now do not inherit from Aspect_PixMap and deprecated.
ToPixMap methods now retrieve Image_PixMap as argument.
Conflicts:
src/ViewerTest/ViewerTest.cxx
Remarks applied
Fix compilation (correct merging error)
Eliminated Aspect <-> Image cyclic dependency
Fixed GIF dump in case of BGR32 image format
