[Lcms-user] Use cmsLinkTag when TransferFunction[1-2] is NULL

[Richard H. <hug...@gm...>]

Typically when creating profiles you have a transfer function set up like this:

transfer[0] = cmsBuildGamma (NULL, 2.2);
transfer[1] = transfer[0];
transfer[2] = transfer[0];

and then do something like cmsCreateRGBProfile(transfer). I don't
think LCMS notices this, and embeds 3 copies of the parametric curve
into the profile. Using the attached patch means if we use the same
curve for all channels then this is only embedded once and we instead
link to the same data area in the profile header. The patch is lightly
tested, and probably needs a sanity test case in the check program.
Using this patch makes the generated profiles smaller.

Comments welcome, thanks.

Richard