* error-message which explains how to run on py2 / older py3
when trying to run from source
* check compatibility between jinja2 and cpython on startup
* verify that webdeps are present on startup
* verify that webdeps are present when building sfx
* make-sfx.sh grabs the strip-hints dependency
* 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
* when deleting files, do not cascade upwards through empty folders
* when moving folders, also move any empty folders inside
the only remaining action which autoremoves empty folders is
files getting deleted as they expire volume lifetimes
also prevents accidentally moving parent folders into subfolders
(even though that actually worked surprisingly well)
* winscp mkdir failed because the folder-not-found error got repeated
* rmdir fails after all files in the folder have poofed; that's OK
* add --ftp4 as a precaution
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