Histogram refactoring
Prefer gboolean
Merge pull request #511 from LebedevRI/histogram-refactoring

Histogram refactoring
Usermanual: mention slideshow view and overwrite on export
ImageIO Format PFM: fwrite one line at a time (based on series of performance measurements)
Collect images: allow collecting by geotagging (is coordinates set)
zonesystem: make the preview more consistent; should fix #9916
Merge branch 'master' of ssh://github.com/darktable-org/darktable
Free memory allocated by dt_alloc_align() using dt_free_align(), not free()
Merge pull request #526 from LebedevRI/pfm-speed

PFM: change write algo
usermanual: start work on version 1.5
Merge pull request #537 from LebedevRI/colollect-geotagging

Collect images: allow collecting by geotagging
Get rid of a hard coded array size
Update French translation.
No need to handle tagxtag since we are using triggers.
No need to alloc them each time, let's use stack here + fix 2 big leaks
cleanup_pipe(): prevent potential double free by setting free()'d pointers to NULL
Cleanup cmsDeleteTransform() calls a bit
Add dt_ prefix to non-static histogram fucntions
usermanual: minor updates and additions