* all: - added a boolean "seekable" object variable to p_input.

* all: - added a boolean "seekable" object variable to p_input.
 (becarefull, it's just if you can seek or not, and not if you have to
 display the progress bar, for thet last you have to check if "position"
 value get != 0.0 )
       - added "audio-delay" and "spu-delay" object variables to delay
 audio/spu to the video. They can be changed on the fly (untested).
       - renamed INPUT__GET/SET_SUBDELAY into
 INPUT_SET_SPU_DELAY and added INPUT_SET_AUDIO_DELAY
 (wrapper to "audio-delay" and "spu-delay")
 - readded INPUT_ADD/GET_INFO/INPUT_SET_NAME. Becarefull to not over-use
them, a demuxer should export DEMUX_GET_META and not using them.