linux v4l2 camera driver unit test, grab stream into a jpeg picture on you file system

"uvc_stream" is a command line application to stream JPEG files over an IP-based network from the webcam to a viewer like Firefox, Cambozola, Videolanclient or even to a Windows Mobile device running the TCPMP-Player.

Our source struct for directing jpeg to our stream object.

jpeg库，是摄像头移植mjpg-stream的重要组成部分(JPEG library is an important part of camera porting mjpg-stream)