Make it clear that it doesn't take ownership of the sample.
https://bugzilla.gnome.org/show_bug.cgi?id=795150
* previous caps that were set on appsrc will be replaced by the caps
* associated with the sample if not equal.
*
+ * This function does not take ownership of the
+ * sample so the sample needs to be unreffed after calling this function.
+ *
* When the block property is TRUE, this function can block until free
* space becomes available in the queue.
*