OSMF SVN

The end result is that RTMP and HTTP stream switching now use the NetStreamSwitchingManager, rather than RTMP using the former and HTTP using internal switching logic. Still need to determine whether to remove HTTPNetStream's switching logic, or keep there for other use cases. Note that we still need to extract HTTPNetStream's switching logic into one or more switching rules (that's phase 3, still to come). Doing so might involve modifying the MetricsProvider to take into account any variations in metrics between RTMP and HTTP.