Initially discussed in the comments to bug 582228.

To properly support TRANSFER_CONTAINER and bare C arrays-of-(objects), we should refactor the release code to implement a post-invocation cleanup list.  Cleanups are something like:

struct _Cleanup {
   enum { CLEANUP_G_FREE, CLEANUP_G_OBJECT_UNREF, CLEANUP_GI_TYPE, ... } type;
   gpointer data;
}

The CLEANUP_GI_TYPE argument uses the existing GI type-driven release method, since that is necessary in any case to release TRANSFER_EVERYTHING out-parameters.

When marshaling container types from JavaScript to C, we can add cleanups for the contained objects (unless TRANSFER_CONTAINER or TRANSFER_NONE) as we add them to the container and then add a clean up for the container (unless TRANSFER_NONE).