misc/objects.c: Make sure vlc_object_get won't return free-ed objects, by doing an atomic refcount decrease and object removal from the object list bank.

contribs/extras: Compensate for shortfalls in ffmpeg's svn repository.  Will submit shortfalls as bugs + patch back to ffmpeg dev team.

cmake: Try to compensate for new ffmpeg directory structure by setting HAVE_LIBSWSCALE_TREE if swscale.his found.

misc/objects.c: Print more info about what was the parent or what were the children if vlc_object_destroy() failed.

contrib/src/Makefile: Checkout CMake project into 'cmake' subdirectory, set up code for downloading cmake directly from archive for future use.

fix that flv muxing issue, and doesn't seem to cause regression. fixes
#1285. Please notify if you notice something broken after this.

src/playlist: Fix a rare memleak that could happen when the interaction is created earlier than expected. (Fix vlc_object mem leak that happen when no module is loaded).

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).

cmake: Code clean up, set up options before we start including custom macros, add CONTRIB_INCLDE to CMAKE_REQUIRED_INCLUDES if ENABLE_CONTRIB is set, and correctly discover postproc/postprocess.h header by temporarily adding FFmpeg_CFLAGS to CMAKE_REQUIRED_FLAGS before checking for the header.

XvMC: remove warnings. The compilation problems lies in a confustion between subpicture_data_t from spudec.h and subpicture_sys_t. No idea how to fix.

XvMC: Compile Fixes, b_shm removal, and obvious typos... subpicture_sys_t still undeclared, no idea why it is around...