Kudoz to sam and Meuuh

Note, this commit may create some assert in previously working code. That does mean that this code wasn't properly working, and that it lacks a PL_LOCK. I prefer nice assert() over races.

Should fix #1708 (Adding a folder in the Mac OS X VLC *media library* result in an assertion failure). Thanks to upcoming commit "playlist: Use PL_ASSERT_LOCKED where the playlist lock should be held.".

playlist: Hold the lock at creation time to conform to playlist_NodesPairCreate requirement to have the pl lock held.

playlist: Use PL_LOCK_IF and PL_UNLOCK_IF to perform some more checks on lock state. And fix a unlocked usage of get_current_status_item().

That may fix or help to fix some input item leaks.

Test for the right thing before tring to do anything.
Check malloc return value (fix potential segfault).

Fix #1704

playlist: Don't export playlist_ItemNewFromInput as it is not used, and don't use pl_Yield from here.

Regression if I recall well.

This might requires some other adjustements.

of teletext buttons every time there was a subtitle track.