Parse the ASMRuleBook SDP line to dynamically create one new AVStream for

Parse the ASMRuleBook SDP line to dynamically create one new AVStream for
each "rule" described in the ASMRuleBook. Each rule represents a stream
of identical content compared to other streams in the same rulebook, but
with a possibly different codec/bitrate/etc. See "[PATCH] rdt.c: ASM
rulebook parsing and AVStream creation" thread on mailinglist.

Originally committed as revision 16466 to svn://svn.ffmpeg.org/ffmpeg/trunk