Squashed 'src/leveldb/' changes from aca1ffc..ae6c262

ae6c262 Merge branch 'leveldb' into ripple-fork
28fa222 Looks like a bit more delay is needed to smooth the latency.
a18f3e6 Tidy up JobQueue, add ripple_core module
ab82e57 Release leveldb 1.12
02c6259 Release leveldb 1.11
5bbb544 Rate limit compactions with a 25ms pause after each complete file.
8c29c47 LevelDB issue 178 fix: cannot resize a level 0 compaction set
18b245c Added GNU/kFreeBSD kernel name (TARGET_OS)
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: ae6c2620b2ef3d5c69e63dc0eda865d6a39fa061
Merge commit 'adae78ea9940f4d44382967d1296e7db0b54a4de' into leveldb-squashed
Merge pull request #2702 from vinniefalco/leveldb-subtree-at-1-10-0

Leveldb subtree at 1 12 0