Users with library:read_own saw every folder anyone had made, and the
folder counts and activity times included other users' files. Folders
now have an owner. A read_own user sees their own folders, shared ones,
folders holding their files and the parents leading there, and adds
files only to their own and shared folders. Admins can share a folder
with everyone. Owners can rename their folders and delete them when
everything inside is theirs.
On upgrade, a folder whose files all belong to one user becomes that
user's; every other folder is shared, so it stays visible as before.
maziggy
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