DynamicSignal: use NativeType property instead of doing unsafe pointer trickery
DynamicSignal: use NativeType property instead of doing unsafe pointer trickery

(which doesn't work with MS csc)

https://bugzilla.gnome.org/show_bug.cgi?id=788132

gstreamer-sharp/gstreamer-sharp,gstreamer-sharp/gstreamer-sharp,GStreamer/gstreamer-sharp,gstreamer-sharp/gstreamer-sharp,GStreamer/gstreamer-sharp,GStreamer/gstreamer-sharp