* include/input_ext-intf.h : added stream_t member to input_thread_t.

 * modules/demux/* : use the stream_t from input_thread_t.
 * include/ninput.h : begin to add new way to register es. (unused for now).
 (in the long term I want to split input_thread_t and intoduce demux_t and
 access_t and perhaps something like access_demux_t)