Fix expand-manifest
Convert expansion tests to toRDF tests

This should improve toRDF coverage considerably as most corner cases are covered by the expansion tests. This probably test some things multiple times but I think that doesn't really matter.

@dlongley @gkellogg could you please run your implementations against these tests to make sure that we agree on the results

I'm fine with reverting this change (once Dave and Gregg cross-checked the results) if someone thinks that this blows the test suite up too much
Add toRDF corner-case test (native "integer" type-coerced to xsd:double)