Pascal Obry

@AlicVB : When you have some free cycle for a review :) TIA.

> removing the thumb->rating = 0 line This needs to be properly tested to ensure there is no side effects. We maybe depends on the rating being 0 to report...

Rescheduled for 5.2.

Likewise, I think wavefrom is probably the best but I'm not sure not using the good old histogram that everyone knows by default is a good idea.

@ralfbrown : But if we change I think it should be for waveform. I'm not sure RGB Parade is better. But again I'm open to any discussion about this change....

About 2. I'm not sure it would make a difference about the self->locked place. The only code in `undo.c` using `self->locked` is: ``` if(!self->locked) { LOCK; ``` So if self->locked...

About 3. Because the only place where `dt_undo_iterate_internal()` is called in inside `dt_undo_iterate()` and there we LOCK & UNLOCK around the call.

Ok, about 3 I was wrong it is also used in `history.c`. This is a refactoring done long time ago... Maybe we can use the locking version of this routine...

> Just seems like poor and unexpected user experience, which is probably why it has been raised multiple times. And nobody came with a fix. Are you willing to work...

> $(VERSION_IF_MULTI/[0-9]/_&/) This is already supported, see: https://docs.darktable.org/usermanual/4.6/en/special-topics/variables/#string-substitution