cubicweb-vcsfile #2818312 make it possible to disable the refresh-repos hook [validation pending]

we have setups where multiple instances share a local cache. only one of them should be in charge of updating the cache, which is not possible currently.

prioritynormal
typebug
done in1.12.3
load left0.000
closed by#9df015142698 hook: if check-revision-interval is negative, don't touch the local cache
patchhook: if check-revision-interval is negative, don't touch the local cache [applied]