moved the branch (for new oids) back to trunk

For anyone interested, I've moved the branch I was working on (ISIS-214)
back to trunk.

The CI build last night caused a few test failures (it was green on my
local workspace), so I'll try to address these.

What I still want to do is to write some contract tests for the objectstore
API (I think we have a JIRA ticket for that somewhere) to get some more
confidence that this refactoring has not introduced any regressions (cos: I
suspect it probably has).  I'll tack away at that too, but now in trunk
rather than in a branch.

Dan