Fixed issue with case conflict detection on creation.
Fixed issue with case conflict detection on creation.

When invoking creation, the transition logic needs to invoke the
ensureNotExists function for each node being created, not just at the
root. The existing behavior for removals is correct.

This commit also cleans up ensureRouteWithProperCase to use more
idiomatic Go. I'm not sure why it had the form that it did.

havoc-io/mutagen,havoc-io/mutagen