unref and copy functions are sometimes used as function
pointers for example in the case of g_hash_table_new_full
as a GDestroyNotify function.

Currently GstBuffer, GstEvent, GstMessage and GstQuery
define their respective unref and copy functions as
macros, making use of gst_mini_object_unref/copy.
This approach works very well for most cases, except
for some automatically generated bindings (currently Vala),
where the memory management semantics are defined
declaratively.

The possible solutions would be to either convert all
the macros into static inline function, or change the
signature of gst_mini_object_unref to take a void*
instead of a GstMiniObject*.

Fixes bug #572480.