Increases the frame reference counting.
The function isn't thread safe, which means you should call to this function from several threads. In is safe to call this function on every place you receive a frame (second and first level invocation handler).
Calling to vortex_frame_free when no reference count was increases is the same as calling to vortex_frame_unref. This means that code written against Vortex Library 0.9.0 (or previous) will keep working doing calls to vortex_frame_free.