video_filter/canvas: various aspect-ratio related fixes

 - Remove silly defaulting to 4:3.  Instead, compute PAR based
   upon SAR of input video and canvas size.
 - Update documentation to remove ambiguity over what is meant
   by aspect-ratio
 - Fix subpicture calculations to
    (a) be much simpler,
    (b) correctly calculate width and height
Signed-off-by: Ilkka Ollakka <ileoo@videolan.org>

Revert previous simplification.

(This is a bit hackish as the conversion is not completed)

It did not really work since VLC 0.9. Also, it was meant for use with
vlc_object_get() and the antique VLC_*() functions which are gone.

And bumping autoconf version seems to be a bit much for such a small improvement

This still uses CMake, because I am still lazy.
This has been tested on Linux, but I would like to port it to win32 (and so CMake might not be the best)
This is basically a copy of the KDE-playground code and started as the GSoC of last summer

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

As I understand this has been a temporary workaround for libvlccore, which seems to have been resolved.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

New protected field bool PLItem::b_is_node to have the data at hand.
Then only check this field in PLModel::flags().
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

Simplify UPnp detection
Simplify goom2k4 detection