Deletions at immutable leaves weren't really deleting anything

Dependencies

• [2] OFINGD26 implementing prev() on cursors (+ some cleanup)
• [*] H3FVSQIQ Unsized pages
• [*] OP6SVMOD Resetting history
• [*] UAQX27N4 Tests
• [*] X3QVVQIS More debugging (del seems to work now)

Change contents

• edit in sanakirja-core/src/btree/page_unsized.rs at line 177
  [2.1097]

  [4.7854]
  + let (_, s1) = s1.split_at(1);
• edit in sanakirja-core/src/btree/page_unsized.rs at line 184
  [2.1161]

  [4.8202]
  + let (_, s1) = s1.split_at(1);
• edit in sanakirja-core/src/btree/page.rs at line 192
  [2.5570]

  [5.14932]
  + let (_, s1) = s1.split_at(1);
• edit in sanakirja-core/src/btree/page.rs at line 199
  [2.5634]

  [5.15312]
  + let (_, s1) = s1.split_at(1);
• edit in sanakirja/src/tests.rs at line 155
  [7.9807]

  [7.9941]
  + }

  +

  + #[test]

  + pub fn del_leaf() {

  + env_logger::try_init().unwrap_or(());

  + let env = Env::new_anon(409600000, 1).unwrap();

  + let mut txn = Env::mut_txn_begin(&env).unwrap();

  + let mut db: Db<u64, u64> = create_db(&mut txn).unwrap();

  + let n = 20 as u64;

  + let i0 = 10 as u64;

  + let mut values = Vec::with_capacity(n as usize);

  + for i in 0..n {

  + put(&mut txn, &mut db, &i, &i).unwrap();

  + if i != i0 {

  + values.push(i);

  + }

  + }

  + let db2 = fork_db(&mut txn, &db).unwrap();

  + del(&mut txn, &mut db, &i0, None).unwrap();

  + assert_eq!(

  + btree::iter(&txn, &db, None)

  + .unwrap()

  + .map(|kv| *kv.unwrap().0)

  + .collect::<Vec<_>>(),

  + values

  + );