[babl] (9 commits) Non-fast-forward update to branch wip/pippin/inverted-cmyk

[Øyvind "pippin" Kolås <ok src gnome org>]

The branch 'wip/pippin/inverted-cmyk' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  c3683c2... use inverted components in CMYK extension
  d359ea5... add more proper cmyk extension

Commits added to the branch:

  7143913... babl_space_get_icc: permit passing NULL for return length (*)
  49df3a0... babl-image: thread-proof single item cache of babl-images (*)
  bee0f4d... babl: permit registering model conversions for non-rgb mode (*)
  5a0eac5... use inverted components in CMYK extension
  39b3ae7... add more proper cmyk extension
  b8c1cd2... cmyk: register model conversions to/from cmykA
  877b77c... lcms experiments
  085345f... lcms / icc integration for cmyk
  9620f6a... reference: some cmyk based to rgb based formats go through 

(*) This commit already existed in another branch; no separate mail sent