More WIP.
More WIP.
More WIP: graph-wrapper tests now passing.
Update transaction API to TK3.

Although we implement transaction support here, the only test we have for it
is test using a mock graphdb. While studying TK3 for other changes, I noticed
some changes that should be reflected in the mock. But I am pretty sure that
more changes will be necessary before transactions are full supported.
More WIP: first pipeline/traversal tests.