Don’t try to merge the formats if ffmpeg or avconv are not installed
This avoids problems with very long URLs.
Apparently, swf players are no longer in use. If we find one, we'll readd it.
If the url doesn’t specify the protocol we can’t directly use it to download the webpage, we would need to build a new url. Instead, we let the generic extractor add the protocol.
Added franceinterIE import to reflect addition of FranceInter support. Issue #2105