Fixes #2517

It is related to #1122 and #1848.

Fixed by Pierre Ynard

This is a bit ugly but it fixes two race conditions:
 - loading plugins while another thread is initializing,
 - using the bank when the first thread has not completed loading plugins.

Unfortunately, there is still a small race when module_need() calls
AllocatePlugin(). It really should not -need to- do that, but the fix would
be quite invasive. We would basically need to store plugin callbacks by names
rather than function pointers. Then the module descriptors would be fully
serializable, so we would not need to re-describe plugins when loading their
shared object. That would also fix the last known corruption bug in the plugins
cache.

If we ever to reintroduce builtin modules, we anyway would need to
rewrite that part.

The attached patch fixes transcoding from mpeg2 with last VLC from git.

jupiter@~/vlc> ./vlc file.ts --sout
'#transcode{vcodec=mp4v}:std{access=file,mux=ts,dst=/dev/null}' -I
dummy
[...]
[0x212d9c0] libmpeg2 decoder debug: 720x576 (display 720,576), aspect
768000, sar 64:45, 25.000 fps
[0x212d9c0] main decoder warning: can't get output picture
[0x212d9c0] libmpeg2 decoder warning: invalid picture encountered
[0x212d9c0] main decoder warning: can't get output picture
zsh: segmentation fault  ./vlc file.ts --sout  -I dummy
Signed-off-by: Rémi Denis-Courmont <rdenis@simphalempin.com>

This was done for no obvious reason in the past... Additionally, this fixes proper version information display in the Finder's Information panel.

Not needed anymore since we are back at linking modules with libvlccode.

This reverts commit 937e3f2f.

* Rename i_playing to is_playing
* Handle case of p_md being NULL.

When the plugin fails to open the framebuffer, then the mmap might
not have been done yet. In this case a segmentation fault will occur
when memset is called on p_sys->p_video. (p_sys->p_video is either NULL,
or MMAP_FAILED.)