Additional usage of the new api

Additional usage of the new api

	* src/media/media-ffmpeg.c (media_ffmpeg_open_file): Use
	avformat_open_input and avformat_find_stream_info,
	avformat_close_input.
	(stream_open): Use avformat_open_input.
	(media_ffmpeg_close): Use avformat_close_input.
	(media_ffmpeg_open): Use avio_size, avformat_find_stream_info,
	av_dump_format and avoid warning.
	(new_media_ffmpeg_read): Use avformat_close_input.

	* src/media/media-ffmpeg.h: Include avcodec.h

	* m4/sxe-mm.m4 (SXE_MM_CHECK_FFMPEG): Verify availability of all
	the included ffmpeg headers. And additional functions,
	avio_alloc_context, avio_size, av_dump_format.
	(SXE_CHECK_FFMPEG_HEADERS): Check also for avcodec.h
	(SXE_CHECK_FFMPEG_LIBS): Check for av_dump_format,
	avio_alloc_context, avio_size.

Signed-off-by: Nelson Ferreira <nelson.ferreira@ieee.org>