Hi,
   I was trying to get print out the caps of a sample of a Gst::AppSink to understand what it is giving me and I uncovered a bug (I think):
In the slot for Gst::AppSink::signal_new_sample():
```
using SamplePtr = Glib::RefPtr<Gst::Sample>;
SamplePtr sample = m_app_sink->pull_sample();
ASSERT(sample);
// Use the C++ API
CapsPtr caps = sample->get_caps();
caps->reference();
ASSERT(caps);

// Use the standard API
//  GstCaps* caps = gst_sample_get_caps(sample->gobj());
```

In the C++ wrapped version, if caps->reference() is not used, then it crashes after 10 iterations or so because the object's ref count goes to zero eventually.
If I add caps->reference(), then the ref count stays even.
I think that the bug is in sample.hg where it's not marked as refreturn but I'm not sure.

Cheers
Ben