Squashed 'src/leveldb/' changes from 7924331..7d41e6f

7d41e6f Merge upstream LevelDB 1.18
803d692 Release 1.18

git-subtree-dir: src/leveldb
git-subtree-split: 7d41e6f89ff04ce9e6a742932924796f69c6e23d
Merge src/leveldb changes for LevelDB 1.18.
Merge pull request #5093

4b0e2d7 Squashed 'src/leveldb/' changes from 7924331..7d41e6f (Pieter Wuille)