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
usermanual: new extended section on geotagging thanks to Rudolf Martin
usermanual: fix for #10079
Don't use GnomeKeyring >= 3.12.0

They broke their API by deprecating the shit out of it and I don't feel
like cleaning up behind them. Merging libsecret support should be the
real fix.
Fix CID 1233591: Misplaced #ifdef
usermanual: update on geotagging panel thanks to Rudolf Martin
colorout: rename misleading high_quality_processing const to force_lcms2

our code already has a real high_quality_processing config property,
using an identical variable for something entirely different is
highly confusing and potentially misleading.
Colorin IOP: prevent crashes in legacy presets update infrastructure
Same as aa9a36330fafe0b965c47c255f52e59e174badab

TODO: go through each reload_defaults() in src/iop/* and fix all similar cases.
Prefer zero initializer over memset

Created using following semantic patch and Coccinelle:

@@
type T;
identifier tmp;
@@
- T tmp;
+ T tmp = { 0 };
- memset(&tmp, 0, sizeof(T));
Cacorrect IOP: prevent crashes in legacy presets update infrastructure
Colormapping IOP: prevent crashes in legacy presets update infrastructure

memset's are not needed. I checked that (at least when using C99 initialization), everything is zero-initialized by default.
Demosaic IOP: prevent crashes in legacy presets update infrastructure
Flip IOP: prevent crashes in legacy presets update infrastructure
Highlights IOP: prevent crashes in legacy presets update infrastructure
Rawdenoise IOP: prevent crashes in legacy presets update infrastructure
Temperature IOP: prevent crashes in legacy presets update infrastructure
Histogram: replace dt_iop_roi_t with new dt_histogram_roi_t