bogus warning about "baseline" mis-parsed creating H.264

Related Debian bug: http://bugs.debian.org/764165

Part of the problem is that both AVCodecContext and the libx264 private data context respond to the "profile" property, but the AVCodecContext does not understand the "baseline" value for profile. The explanation on the Libav FAQ does not exactly apply because our avformat consumer uses 'v' prefix to attempt to do the same thing. However, "vprofile=baseline" still causes the problem in MLT because both video contexts still respond to "profile" (v prefix stripped) but only one understands "baseline." Somehow, avconv avoids this problem based upon some kind of difficult to follow logic.

I think part of the problem also stems from the fact that that MLT chooses to be compatible with many versions of Libav and FFmpeg, and the way I implemented mlt_property->AVOption makes it difficult to do something like "do not apply this property to the AVCodecContext if the codec private context accepted it." Not to mention, I have to fully confirm that is even the correct logic. Otherwise, there could be a situation where a redundant AVOption is not set when it should have been.

So, you see, this is something rather specific and a bit complicated for something that is only classified as a nuisance at this point.

Start by tracing how mlt_property->AVOption applies vprofile=baseline across AVCodecContext and the libx264 private data context, including the avformat consumer behavior described in the issue. No file, test, or entry point is named, so completion would require confirming the correct handling across the supported Libav and FFmpeg versions and reproducing the bogus warning.