Close #6451

Usage: http://localhost:8080/art?item=1234

The slider is not displayed, anyway. But sometimes it flickers through
for a short moment which does not look good.

based on patch by Richard Grenville <pyxlcy@gmail.com>

Note that the origin values can also be negative when we have our window
on a secondary screen.

This fixes playback on an AES-128 encrypted stream I ran into: the key
URL happened to have "iv" somewhere in it, which led VLC to try - and
fail - to parse an IV.
Signed-off-by: Hugo Beauzée-Luyssen <beauze.h@gmail.com>

Coeffs have been recomputed.

Close #6132

There is not that much common code left for the access case, except for
debug messages. The resulting code is a lot easier to read IMHO.
Also I have no way to test the access plugin, so lets split it where it
will not get more broken.

They are mostly used by plugin descriptors.

dirs.c is too simple to grant a file of its own, I think.