autoexport does not handle changes on deleted nodes or properties correctly

Attached a patch file that demonstrates the problem. It adds two test cases to the "new-node" fixture:

• node /deletedInFirst: defined in "topmost", then deleted in "exportFirst"
• node /deletedInFirstSuperfluousDefinitionInSecond: defined in "topmost", then deleted in "exportFirst" with a superfluous (ignored) definition in "exportSecond"

In both cases the expectation is that if the node is part of a diff, it gets exported into "exportSecond".

After fixing this, test cases should also be created for deleted properties, which likely don't work either.