From Mattias Helsing, "The addition of the GStreamer cmake find script broke my build because
cmake vars weren't passed correctly to find_package_handler_args, so
while the find script didn't find a single required GStreamer lib or
include path it still reported GSTREAMER_FOUND=TRUE (and then tried to
compile the new plugin). This fixes it and correctly reports missing
components."


git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14611 16af8721-9629-0410-8352-f15c8da7e697