Fix constant recomputation of preview pipe

This might be a little dirty by just decreasing the chance of the
race condition to hit us. Not sure if proper locking would work though,
see comment in commit.
Updated Dutch translation
Merge pull request #595 from MRIG/master

Updated Dutch translation
cameras.xml: remove extraneous hyphen
Merge pull request #596 from dtorop/cameras-hyphen

cameras.xml: remove extraneous hyphen
build: make it compile without gphoto2 again.
Fix GTK warnings when SVG files can't be loaded
lua : move view_changed event out of the GTK thread
lua : fix shortcuts not working
Update French translation.

For #9988.
lua : add a reset() function for libs
force self->widget to null when a lib's UI is destroyed
lua : add a way to easily know if a lib is displayed on the screeen
Fix infinite reprocess (FIXME: why g->reprocess_on_next_expose == TRUE ?)
IOP Exposure: Deflicker: show what exposure correction have actually been used