macosx: add webm the filetypes handled by the bundle
stream_dvd: prevent segmentation fault with some broken files

I have a sample where some final chapters are missing. This was causing a
segmentation fault when trying to fetch chapter times for them.

This makes the code ignore those chapters.
mplayer: m_option: fix clang -Wformat compiler warning

Code was using %d format instead %zd to print size_t data.
gl_common: signal to GL backend whether we are probing

This is supposed to reduce the amount of useless error messages shown
during initialization of vo_opengl. If multiple backends are compiled,
usually only one of them will work. For example, on Linux both X and
Wayland backends can be compiled, but usually either Wayland or X is
running. Then, if Wayland is not running, but X is, trying to initialize
the Wayland backend should not spam the terminal with error messages.

Code using this should probably raise the log level for error messages
from MSGL_ERR to MSGL_V. Only error messages that are typically printed
in these situations should be changed. For example, if Wayland is
available, but some other part of initialization fails, the error
messages should probably be visible.
x11_common: probing

Not too sure about this. It sucks a bit that I had to add vo.probing.
wayland/common: probing
gl_common: add wayland backend before x11 backend
x11/common: print message according to probing status
wayland/common: print message according to probing status
Removed duplicating message-call in x11/common and wayland/common
wayland/common: use MP_MSG rather than mp_msg