"LinearRaw" is a value that the PhotometricInterpretation tag can be set
to on DNG images that contain color information for all channels instead
of being bayer-encoded ("CFA" value).

The DNG decoder is complete enough that we can enable this now.

Sample:
- http://www.rawsamples.ch/raws/nikon/SCANNER_NIKON_LS5000.DNGSigned-off-by: Nick Renieris <velocityra@gmail.com>