* permission `.` grants dotfile visibility if user has `r` too
* `-ed` will grant dotfiles to all `r` accounts (same as before)
* volflag `dots` likewise
also drops compatibility for pre-0.12.0 `-v` syntax
(`-v .::red` will no longer translate to `-v .::r,ed`)
this carries some intentional side-effects; each thumbnail format will
now be stored in its own subfolder under .hist/th/ making cleanup more
effective (jpeg and webm are dropped separately)
safest way to make copyparty like a general-purpose webserver where
index.html is returned as expected yet directory listing is entirely
disabled / unavailable
* when accessing files inside an xdev volume, verify that the file
exists on the same device/filesystem as the volume root
* when accessing files inside an xvol volume, verify that the file
exists within any volume where the user has read access
mainly motivated by u2cli's folder syncing in turbo mode
which would un-turbo on most dupes due to wrong lastmod
disabled by default for regular http listings
(to avoid confusion in most regular usecases),
enable per-request with urlparam lt
enabled by default for single-level webdav listings
(because rclone hits the same issue as u2cli),
can be disabled with arg --dav-rt or volflag davrt
impossible to enable for recursive webdav listings
