Squashed 'src/leveldb/' changes from 936b461..e991315

e991315 Merge upstream LevelDB 1.15.
0cfb990 Release LevelDB 1.15
02ac9f1 Merge upstream LevelDB 1.14.
0b9a89f Release LevelDB 1.14

git-subtree-dir: src/leveldb
git-subtree-split: e991315d7fe4ca84a98902578106cbffa3dcccfd
Merge src/leveldb changes for LevelDB 1.15
Merge pull request #3405

55c6890 Squashed 'src/leveldb/' changes from 936b461..e991315 (Pieter Wuille)