Update French translation of usermanual
Proof-read till "Velvia and Channel mixer" modules.

Translate in all the manual
  lightness = clarté (of a reflective object)
  brightness = luminosité (of a light source object)
  luminance = clarté

To be consistent with French darktable's GUI I translate "core options" as "fonctionnement" in all the usermanual

A "make update-usermanual-fr" has been necessary to fix the errors due to incorrect uses of hyphens.
First use of poedit 1.5.4 which manages better the lines
Some error corrections in the header of the file fr.po
Merge pull request #667 from VictorLamoine/master

Update French translation of usermanual
exif: disable draconic dmc-gh2 workaround (#10074)
Redo error checking logic for stat()

Reimplements 7cca3bc9326ac3a56d1c70af29fc81939ca37b70
OpenCL: move interpolation functions into separate header
OpenCL: move clip&rotate related stuff into separate file
OpenCL: move lens related stuff into separate file
OpenCL: move interpolation kernel into separate file
OpenCL: move lookup stuff into separate header
OpenCL: refactor clip_rotate_bilinear into interpolation_compute_pixel_bilinear_4f
OpenCL: refactor clip_rotate_bicubic into interpolation_compute_pixel_bicubic_4f
OpenCL: refactor clip_rotate_lanczos2 into interpolation_compute_pixel_lanczos2_4f
OpenCL: refactor clip_rotate_lanczos3 into interpolation_compute_pixel_lanczos3_4f
OpenCL: refactor clip_rotate src pixel coord calculation into function
Needed to fix some manufacturers madness
Scalepixels: new IOP

Needed to fix NIKON D1X non-square pixels madness
Scalepixels IOP: OpenCL
iop_dependencies.py: add scalepixels
Run iop_dependencies.py after merge!
Flip IOP: modify_roi_in(): drop sanity check

Causes garbage when used with scalepixels.
If it is really needed, it should be rewriten in a way, that has no side-effects like that.
wip