if someone accidentally starts uploading a file in the wrong folder,
it was not obvious that you can forget that upload in the unpost tab
this '(explain)' button in the upload-error hopefully explains that,
and upload immediately commences when the initial attempt is aborted
on the backend, cleanup the dupesched when an upload is
aborted, and save some cpu by adding unique entries only
an extremely brutish workaround for issues such as #110 where
browsers receive an HTTP 304 and misinterpret as HTTP 200
option `--no304=1` adds the button `no304` to the controlpanel
which can be enabled to force-disable caching in that browser
the button is default-disabled; by specifying `--no304=2`
instead of `--no304=1` the button becomes default-enabled
can also always be enabled by accessing `/?setck=no304=y`