Improved color aberration auto-correction

 No loss of color saturation
 Smooth sub-pixel color shifts without block discontinuities
 Significantly more accurate measure to estimate color shifts
 The fitting was fixed and improved
 Restriction to radial correction is an option
 The analysis is performed only once per pipe instance
 Restored OpenMP support
 Improved border reconstruction
 Clean code
Merge branch 'master' of github.com:darktable-org/darktable into cacorrect

Conflicts:
	src/iop/cacorrect.c
Merge branch 'cacorrect' into cherries