Not surprisingly, testing the btree code shook out a few bugs
- the treap root wasn't initialized
- existing split source block wasn't compacted
- item movement used item treap fields after deletion
All of these had the consequence of feeding the treap code bad offsets
so its node/u16 casts could lead it to scribble over memory.
Signed-off-by: Zach Brown <zab@versity.com>