[daip] alternative reference values, SPLIT, IMAGR

[Gustaaf van Moorsel]

Dear Daip,

I noticed that whereas SPLIT copies the alternative reference values
from the SU table to the output header, IMAGR, when running directly
on a multisource file, does not.

This means that images that went through the route SPLIT -> IMAGR will
have the alternative reference values in their header, whereas images
created by IMAGR straight from the multisource files do not.  I don't
see a good reason why IMAGR when running on a multisource file could
not populate the alternative reference values in the image header.

Gustaaf