Squashed 'src/leveldb/' changes from ae6c262..676df7b

676df7b Added GNU/kFreeBSD kernel name (TARGET_OS)
3e455c3 Release leveldb 1.12
75d2e20 Release leveldb 1.11
0172636 LevelDB issue 178 fix: cannot resize a level 0 compaction set
6d20fc8 CondVar::SignalAll was broken, leading to deadlocks on Windows builds. http://code.google.com/p/leveldb/issues/detail?id=149
f90d088 Upgrade LevelDB to 1.10.0, mostly for better write stall logging.
REVERT: ae6c262 Merge branch 'leveldb' into ripple-fork
REVERT: 28fa222 Looks like a bit more delay is needed to smooth the latency.
REVERT: a18f3e6 Tidy up JobQueue, add ripple_core module
REVERT: ab82e57 Release leveldb 1.12
REVERT: 02c6259 Release leveldb 1.11
REVERT: 5bbb544 Rate limit compactions with a 25ms pause after each complete file.
REVERT: 8c29c47 LevelDB issue 178 fix: cannot resize a level 0 compaction set
REVERT: 18b245c Added GNU/kFreeBSD kernel name (TARGET_OS)
REVERT: 8be9d12 CondVar::SignalAll was broken, leading to deadlocks on Windows builds. http://code.google.com/p/leveldb/issues/detail?id=149
REVERT: c9fc070 Upgrade LevelDB to 1.10.0, mostly for better write stall logging.
REVERT: 8215b15 Tweak to variable name to support unity build

git-subtree-dir: src/leveldb
git-subtree-split: 676df7ba27992e8e7e42cbd81cabe3710a86a1d3
Merge commit '6bfc81accedcc7fffb2f8414a5f9ed6ff574aed1'