Fix #4479
See https://bugs.kde.org/show_bug.cgi?id=279973

Sometimes fonts are muxed with the wrong MIME type, but we should
still be able to use them. Especially OpenType font collections are
affected by this. Match attachments by extensions .ttf, .otf and .ttc
in addition to MIME type to fix these issues.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Add a message callback function to get libass messages into VLC's
logging system.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

 - command line help text
 - text domain binding

No need to load the config file twice anymore.

This must be a bug in the SDK, so better ignore the header.

don't start variables with _, they have local scope anyway

This avoids allocating memory and formatting debug messages when none
of the subscribers care about them.

This fixes compilation with newer Mingw-w64.

It was removed over 6 years ago.

We have enough static locks in libvlc, I think: the
configuration R/W lock, the module bank mutex, the system-specific
initialization mutex, the message subscription R/W lock, the sets
of mutexes for initializations of specific libraries, the LibVLC
thread variable mutex, the configuration file mutex, the PRNG mutex,
the object pipe mutex, the object name mutex, the dialog provider
mutex, the interface module registration mutex, the OSD mutex, the
VLM mutex, the HTTP hosts mutex and the OSD mutex...