A string statement is not a docstring if it doesn't occur right at the top
of modules, functions, class definitions etc.
This patch fixes it.
Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
Each source of videos have a different extraction process, they are in different methods of the extractor.
Changed the extension of videos from mp4 to flv.
I changed the ExtractorError from ```msg = msg + u'; please report this issue on http://yt-dl.org/bug'``` to ```msg = msg + u'; please report this issue on http://yt-dl.org/bug with the complete output by running the same command with --verbose flag'```
Hopefully this will tell the users to report bugs with the complete output.