Fix ticket #3958

Signed-off-by: Ilkka Ollakka <ileoo@videolan.org>

A socket is leaked when the client passes a wrong session identifier.
A remote attacker could craft malicious RTSP requests and...

This way we can implement both a search function and a description function.

So that you don't kill the lua.sd search() functions

Adds a driver for the BlackMagic DeckLink series of SDI cards (input only).
It requires BlackMagic's proprietary (but free-to-download) SDK to compile
and run. I've only tested it on Linux -- the Windows API is very similar but
not identical, so some adjustments will probably have to happen if anybody
wants this to work on Windows. (Windows users can, AFAIK, already access the
card via DirectShow, though.) It supports multiple cards, all the various
A/V inputs and video modes including setting field dominance and multichannel
input (2, 8 or 16 channels).

All testing has been with a DeckLink HD Extreme 3, which I have very
graciously been given access to by Frikanalen.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

This adds exactly NOTHING to the usefulness of the UI

Changing the choice list of a configuration item is not thread-safe.
Plus it does not make much sense to use a strict choice list if the
choices change dynamically.

If ever needed, we can invent a suggestions list system later, just
like we already do for SD plugins enumeration.

This was only used by {alsa,oss}-audio-device and not semantically
correct anyway. If we deem that this is useful, we should register
a callback on the corresponding variables and change the variables
from the UI, not the process-wide configuration.

This was only used to change the OSS or ALSA device on the fly.
However, this really should be done with a variable callback, not from
the configuration.