Data dithering should be configurable

[LibRaw]

For precise raw data inspection it is vital to have data dithering configurable, because unaltered RAW data are very informative for many cases:

• regular histogram holes indicates real camera 'bit count'
• not so regular holes indicates different kinds of 'data cooking' within camera (e.g. Nikon's WB preconditioning, or several kinds of lens corrections/etc)