Since 23 September 2011 Aurora distribution (from an OpenEmbedded point of view) as been dissolved and merged in SHR as a simple image.
This is much simple for everyone.
So since now, to build Aurora, all you have is to follow this SHR manual except that instead of building "shr-image" you build "aurora-image".
bb -k aurora-image
That is all.
Don't forget to change the MACHINE in your setup-local file as it come set to om-gta02 by default.