In the generated libgimp wrappers, we can't return object arrays
from a call to GIMP_VALUES_DUP_OBJECT_ARRAY() because it returns
a deep copy and adds a reference to all objects, which the caller
would have to unref.

But we want a shallow (transfer container) copy because we don't want
libgimp proxy objects to be refed or unrefed by any user code.

Therefore, add a HACK that simply memdup()s and returns the
GimpObjectArray's array memory, and leaves the contained object
pointers alone.