Batch reuse and idempotence

[pgera]

The following do not work:

1. Idempotence: G.delete(batch); G.delete(batch);
2. Reuse: G1.insert(batch); G2.insert(batch);

If you want to delete some edges from a graph and insert them into a new graph, you should be able to reuse the same batch as G_new.insert(batch); G_orig.delete(batch);

The current workaround for this issue is to create a different batch from the same COO pointers. That works.