Add support of url without protocol defined

[skyghis]

http://www.spi0n.com/zap-spi0n-com-n216/

I try to download the video at given URL, youtube-dl says:

ERROR: no suitable InfoExtractor for URL //www.dailymotion.com/embed/video/k2mm4bCdJ6CQ2i7c8o2

If I add the missing http in front of the URL in the error message, I can download the file.

$ youtube-dl --version
2014.04.21.6

Thanks in advance.