Added Image::g/setOrigin to help movie plugins tell applications that the imagery

is not the usual OpenGL BOTTOM_LEFT orientation, but with the origin TOP_LEFT.  This
allows geometry setup code to flip the t tex coord to render the movie the correct way up.

src/osgPlugins/quicktime/QuicktimeImageStream.cpp

@@ -42,6 +42,8 @@ int QuicktimeImageStream::_qtInstanceCount = 0;
 // Constructor: setup and start thread
 QuicktimeImageStream::QuicktimeImageStream(std::string fileName) : ImageStream()
 {
+    setOrigin(osg::Image::TOP_LEFT);
+
     _len = 0;
     _movieData = new MovieData();