misc/objects.c: Don't rely on vlc_object_destroy() to destroy objects, but...

misc/objects.c: Don't rely on vlc_object_destroy() to destroy objects, but expects vlc_object_release to do it when the refcount goes to zero.
* Meaning, that when created objects gets a refcount to 1.
* Destroying is instantaneous and we don't have to poll for a few secondss or so to wait until the object's refcount reach 0.
* We now track vlc_object_t's mem leaks when libvlc_global is released (Hard error for now, so they don't get unoticed)
* We fail hard if an object is released with a refcount of 1 without being detached from its parent and its children, to make sure such cases don't go unoticed.
(make test or make check still pass after that one. VLC is known to leak one object when no module is loaded, this must be fixed).