On all my linux PC (debian sid and lenny) it has really bad side effects,
mostly when seeking and at startup up (slow or even blocking), and makes
sshfs unusable.

fontconfig doesn't really seem to set that result variable correctly
in allmost all cases, only few codepaths that it's setted to NoMatch,
but it doesn't get setted on valid paths or configerrors or any of
thosecases. Thanks to Laurent Aimar for this one.

Add:
- http-user-agent
- ps-trust-timestamps
- vout-event
And some rtsp options (username, passwd)
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

I don't know if this is really useful. On Linux it is not really useful
given the libtool versioning algorithm (VER:REV:AGE -> VER-AGE:AGE:REV)
ensures different sonames in any case.

This reverts commit 17eb17c5.

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

Signed-off-by: Laurent Aimar <fenrir@videolan.org>

Should be backported.

 * print a warning when var_DelCallback can't find the callback because the
   data doesn't match
 * these warning are only for debug builds.