Add support for JPEG input in cjpeg
Fix issue with JPEG read in cjpeg

Color space and sampling was not properly configured leading to errors
when encoding from a JPEG file.
Improve support of JPEG input in cjpeg

Add macro JPEG_RAW_READER that defines whether to pass RAW sample data
from input to output JPEG files (hence preserving color space and
sampling). Macro is now disabled by default.
Add code to copy metadata from input to output JPEG, hence preserving
color profiles and other important information
Merge branch 'jpegin'
Silence compiler warning