oxenstored: allow self-conflicts

oxenstored: allow self-conflicts

We already avoid inter-domain conflicts but now allow intra-domain
conflicts.  Although there are no known practical examples of a domain
that might perform operations that conflict with its own transactions,
this is conceivable, so here we avoid changing those semantics
unnecessarily.

When a transaction commit fails with a conflict and we look through
the history of commits to see which connection(s) to blame, ignore
historical commits that were made by the same connection as the
failing commit.

Reported-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Thomas Sanders <thomas.sanders@citrix.com>
Reviewed-by: Jonathan Davies <jonathan.davies@citrix.com>