Media Source for FLVs

Get the media source implementation working for FLVs. Currently, they play but the big play button stays up the whole time. Some changes are necessary to the video.js SWF-- see my media-source branch for that. Attempt to delegate to the native media source implementation if it's around. You'll need to provide your own copy of an FLV and video.js and the video.js swf to try this out.