Assign the x-pf-asf payload string to be decoded by rtp_asf.c, and add a

SDP line handler that parses the streamID in the SDP so that ASF stream
data can be matched to their respective streams in the RTSP demuxer. See
"[PATCH] RTSP-MS 12/15: ASF payload support" thread on mailinglist.

Originally committed as revision 18061 to svn://svn.ffmpeg.org/ffmpeg/trunk