Squashed 'src/leveldb/' changes from a02ddf9..be1b0ff

be1b0ff On Mac OS X fsync does not guarantee write to disk. Use fcntl F_FULLFSYNC instead.

git-subtree-dir: src/leveldb
git-subtree-split: be1b0ff1fcd6ad820a7fd111ac671fb51cc68001
Merge leveldb subtree change.

* On Mac OS X fsync does not guarantee write to disk. Use fcntl F_FULLFSYNC instead.
Merge pull request #2916 from sipa/leveldb-osxfsync

Import OSX fsync change from LevelDB subtree