support for adding new components (syntax: ffmpeg -i input_file [output...

support for adding new components (syntax: ffmpeg -i input_file [output options] output_file [[component output options] {-newaudio|-newvideo|-newsubtitle}]... - added subtitle support - added '-alang' option

Originally committed as revision 4351 to svn://svn.ffmpeg.org/ffmpeg/trunk