* src/input/input_dec.c, include/vlc_codec.h: added 2 callbacks in the decoder_t structure for pictures linking/unlinking.
* modules/codec/libmpeg2.c: restored pictures linking/unlinking code.
* modules/codec/ffmpeg/video.c: idem and reenabled direct rendering even when the hurry-up mode is activated as it doesn't seem to create a problem anymore with recent ffmpeg.