  This paper has been withdrawn, not because of any errors (that we know of),
but because rather than presenting our material as a series of 3 papers, as we
originally intended, we have now combined them into one long paper, which is "A
theory of generalized Donaldson-Thomas invariants", arXiv:0810.5645v3, June
2009, 181 pages, and this paper has been incorporated into that.
