* remove unneded p_sys variables (p_xml)
* fix memleaks.
* fix object leaks.

It previously assumed TRUSTED.
No functionnal/security changes in this commit.

This improves readability a lot and prevent us from reinventing the wheel.

Missing some cases that I could not test.
Also ffmpeg/chroma.c is locked, so I can but leave it broken.
Fix is for the remaining modules is obvious and the issue is easy to detect.

You can not change a playlist_item_t to be a node, when you previously registered events on it, using input_item_t sub items adding event, because the pointer will be destroyed.
If you want to use nodes anyway, you have to explicitely create them.
Note: we were lucky that xspf did work so far, because we were EXCLUSIVELY using invalid pointers, except for the 1st item being added to each playlist_item_t (it did happen before the conversion obviously).

playlist demuxers: return -1 in case of error, 0 in case of eof, 1 else; like any correct demuxer. (we always return eof since playlists don't need 2 successive demuxing).
fix a corner case bug in ifo.c

Enforce access to input_item_t through input_item_{G,S}et*()
Unlock mutexes before calling these functions
Free strings returned by input_item_Get*()

New functions added:

char * input_item_GetURI( input_item_t  * )
void input_item_SetURI( input_item_t * , char * )

mtime_t input_item_GetDuration( input_item_t * )
void input_item_SetDuration( input_item_t * , mtime_t )

to access input_item_t->psz_uri and input_item_t->i_duration

* Protect input item's meta through setters and getters. That allows tracking of input item meta info changes.
* vlc_meta_t gains a table for accessing its non-extra meta.

  - Return correct item ids
  - Structures for navigating the playlist
  - Consistent locking
* Add a b_locked parameter to the remaining playlist API calls

* Headers in include must contain the structures and prototypes needed
  by the plugins and should be named vlc_*.
* Headers in include/vlc must contain the structures and prototypes
  needed by external libvlc clients

* Moved and renamed some things in headers. 
   - Removed vlc_cpu.h, vlc_error.h (merged in vlc_common)
   - Removed snapshot.h (merged in vlc_vout.h)
   - Removed vlc_spu.h (merged in vlc_osd.h)
   - Removed intf_eject.h and vlc_interaction.h (merged in vlc_interface)
   - Moved all internal headers to src
   - Merged vlc_video.h and video_output.h and move private things to src
   - Removed vlc/intf.h, vlc/aout.h, vlc/vout.h, vlc/decoder.h and vlc/input.h
     (meta headers for use in modules, and often implying too large 
     dependencies)
* Removed some useless dependencies
* Unexported a bunch of functions and structures used only in src/
  (--> Still some work here)
* Finally made input_thread_t and input_source_t (mostly) private. 
  Added input_GetItem to fetch the input_item of an input_thread
* Cleaned up deprecated entries in vlc_symbols.h and bumped up symbol 
  prefix

This commit has a 99% probability of breaking the build, 0.1% of killing
your cat and 0% of getting you hot chicks.

 - Remove a bunch of transition now-useless API.
 - Remove all playlist_Lock* functions. Matching functions now accept a
   b_locked parameter that should be set to VLC_TRUE if the playlist is
   locked when calling the function. The advantages are that it reduces
   the API bloat and that the b_locked flag can be propagated in the
   call stack
 - Remove useless playlist testsuite
 - Remove broken daap plugin (unmaintained wrt VLC API changes, relies on 
   an unmaintained library, probably unable to read content from new itunes, 
   ...). Implementations exist in rhythmbox, xmms2 and 
   daap-sharp, we should see if a proper lib exists or if we could 
   make one
 - Reduce verbosity a bit
 - Documentation

If the item is not to be preparsed but has enough meta, mark it as preparsed

* Remove some unneeded wrappers and locking

* malloc with NULL check
* file extension check
* check if a demux was forced
* try peeking, and check what we poke
* init standard demuxer fields
* create packetizers

What is currently broken:
 * Some playlist demuxers (shout, dvb and pls)
 * DAAP
 * BeOS playlist
 * GPE playlist, I suppose

What has some trouble:
 * Meta handling in several demuxers (most notably TS)
 * Skins2 playlist (doesn't refresh correctly)
 * OS X playlist (see bigben's latest commits)