Squashed 'src/leveldb/' changes from aca1ffc..5bbb544

5bbb544 Rate limit compactions with a 25ms pause after each complete file.
8c29c47 LevelDB issue 178 fix: cannot resize a level 0 compaction set
8be9d12 CondVar::SignalAll was broken, leading to deadlocks on Windows builds. http://code.google.com/p/leveldb/issues/detail?id=149
c9fc070 Upgrade LevelDB to 1.10.0, mostly for better write stall logging.
8215b15 Tweak to variable name to support unity build

git-subtree-dir: src/leveldb
git-subtree-split: 5bbb54456a538445e7507c08e28ae340a848944a
Merge commit '109b32b2968611750cbe722b9ad22262aee7eff5' into leveldb-subtree-at-1-10-0