When freeing one of the collections such as GArray, GPtrArray, GSList,
etc. it is common that the items inside the connections must be
freed/unrefed too.

The previous code often iterated over the collection first with
e.g. g_ptr_array_foreach and passing e.g. g_free as GFunc argument.
For one, this has the problem, that g_free has a different signature
GDestroyNotify then the expected GFunc. Moreover, this can be
simplified either by setting a clear function
(g_ptr_array_set_clear_func) or by passing the destroy function to the
free function (g_slist_free_full).

Signed-off-by: Thomas Haller <thaller@redhat.com>